@DaveDM
Frankly I don't do a lot of sharpening these days and it has been a while since I have used some of these, so I'll be basing this on notes as much as memory.
With the BORIDE stones there seems to be a transition between F220 and F320 in terms of bond. The F320 stones typically perform as expected, whereas I have had trouble with F220 and coarser stones, starting with the stock Edge Pro 220 which for me would not cut unless freshly conditioned and then poorly. I think your interest is on the coarse end so I'll start there.
Coarse stones
The coarsest, fastest stones I have are the stock 120 CS-HD, followed by the CKTG #140 diamond plate. (On wear resistant steel the runner-up is probably 125µ 3M Diamond Microfinishing Film, while scratching less deeply than the #140, but I've only used it once or twice.)
The 120 CS-HD works fast on just about anything given enough pressure but it's really messy (gritty mud) and on a wide bevel getting enough pressure can take serious force. These days I avoid it by thinning freehand on wet/dry sandpaper (3M Pro Grade Precision with Cubitron II grit is my current favorite), which gives me a small edge bevel that is easy to work on a finer stone and which cuts a lot better anyway. On very soft, very dull knives—that aren't worth the work of thinning—a coarse hand file is great for ripping in a new bevel; the best solution I found without space for a belt grinder. When these methods are inappropriate the #140 plate gets the job started without the scratchy mud of the 120 CS-HD.
The 120 AS-9 is as hoped much cleaner, but it's also not fast enough. Still if I want to avoid the deep scratches of the #140 it can be useful, but I usually just use one of my F220 stones with more pressure which seem as fast. If I recall some users on a Russian forum compared the AS-9 and T2 stones at low grit and found the T2 better, but neither is a speed champ.
I have yet to find a use for the 150 Ruby despite it being recommended; it sheds a lot of grit (not even mud!) yet manages to cut slowly. I would think that such a soft bond would be useful on really hard steel or very wide bevels but I haven't found that to be the case. It works bone dry better than other stones because the shedding prevents loading, but I don't work dry to avoid breathing dust.
The 150 & 220 T4 (not T2) stones are moderately useful. The 150 acts slower/finer than hoped. They wear somewhat quickly and can shed grit or be gouged, but nothing like the 150 Ruby. They are treated stones and don't like to wet out. Since I have other options I don't use them. Probably better with oil instead of water but I haven't tried.
The 180 & 220 Orange EDM are my choice for simple steels. They don't cut very hard or wear resistant steel but can still be used to remove #140 scratches. They normally wear slowly, but with very soft steel or point pressure (tip work, serrations, strong recurves) wear accelerates; there I prefer 120 AS-9, 220 AM-8 or 320 T2.
The 220 CS-M is my ace for hard steel. This whole series is unmatched for wear resistant steel if like me you cannot afford diamond. They grip with much less pressure than CS-HD. They are soft but not inappropriately so. Also good for very wide bevels on simple steels when other stones start to skate. I don't have a CS-M coarser than 220 because I don't want to deal with a mess like the 120 CS-HD. The 220 CS-M mud is trouble enough at times, so on expensive knives I would start with 320 CS-M or diamond microfinishing film. Were I trying to sharpen for profit again I would get the Matrix stones. Since I am not these will do.
I have 150 & 220 TH stones in 0.125*0.5*6" size. These appear to be a hard version of T4 that doesn't shed grit, and they too act slower/finer than grit number would indicate. I use them by hand for breaking edges.
My newest BORIDE stone is a 220 AM-8 that I profiled to fit serrations. It's a very hard stone that should hold its shape well even under this amount of pressure. (The stock 220 stone that just skates on flat edges actually breaks down fairly quickly when used in serrations.)
Medium stones
I have in the F320 to F400 range, approximately in ascending rank of breakdown: AM-8, T2, TH, AS-9, Orange EDM, Golden Star, CS-HD, CS-M, Sigma Power #700 3F Carbon. As mentioned at the start these all more or less perform as expected for the kind of stone each is, but I'll try to answer any specific questions. Since you asked about the Golden Star: these are very smooth operating stones that feel pleasant to use. They finish finer but on average cut a little slower than the other alumina stones. Their performance seems to depend on the steel a bit more than others (e.g. the unusually consistent 600 Orange EDM, a favorite), sometimes being faster or slower than I would expect from the apparent hardness of the steel alone. Since these appear biased toward finishing I have never tried one coarser than 320.
Frankly I don't do a lot of sharpening these days and it has been a while since I have used some of these, so I'll be basing this on notes as much as memory.
With the BORIDE stones there seems to be a transition between F220 and F320 in terms of bond. The F320 stones typically perform as expected, whereas I have had trouble with F220 and coarser stones, starting with the stock Edge Pro 220 which for me would not cut unless freshly conditioned and then poorly. I think your interest is on the coarse end so I'll start there.
Coarse stones
The coarsest, fastest stones I have are the stock 120 CS-HD, followed by the CKTG #140 diamond plate. (On wear resistant steel the runner-up is probably 125µ 3M Diamond Microfinishing Film, while scratching less deeply than the #140, but I've only used it once or twice.)
The 120 CS-HD works fast on just about anything given enough pressure but it's really messy (gritty mud) and on a wide bevel getting enough pressure can take serious force. These days I avoid it by thinning freehand on wet/dry sandpaper (3M Pro Grade Precision with Cubitron II grit is my current favorite), which gives me a small edge bevel that is easy to work on a finer stone and which cuts a lot better anyway. On very soft, very dull knives—that aren't worth the work of thinning—a coarse hand file is great for ripping in a new bevel; the best solution I found without space for a belt grinder. When these methods are inappropriate the #140 plate gets the job started without the scratchy mud of the 120 CS-HD.
The 120 AS-9 is as hoped much cleaner, but it's also not fast enough. Still if I want to avoid the deep scratches of the #140 it can be useful, but I usually just use one of my F220 stones with more pressure which seem as fast. If I recall some users on a Russian forum compared the AS-9 and T2 stones at low grit and found the T2 better, but neither is a speed champ.
I have yet to find a use for the 150 Ruby despite it being recommended; it sheds a lot of grit (not even mud!) yet manages to cut slowly. I would think that such a soft bond would be useful on really hard steel or very wide bevels but I haven't found that to be the case. It works bone dry better than other stones because the shedding prevents loading, but I don't work dry to avoid breathing dust.
The 150 & 220 T4 (not T2) stones are moderately useful. The 150 acts slower/finer than hoped. They wear somewhat quickly and can shed grit or be gouged, but nothing like the 150 Ruby. They are treated stones and don't like to wet out. Since I have other options I don't use them. Probably better with oil instead of water but I haven't tried.
The 180 & 220 Orange EDM are my choice for simple steels. They don't cut very hard or wear resistant steel but can still be used to remove #140 scratches. They normally wear slowly, but with very soft steel or point pressure (tip work, serrations, strong recurves) wear accelerates; there I prefer 120 AS-9, 220 AM-8 or 320 T2.
The 220 CS-M is my ace for hard steel. This whole series is unmatched for wear resistant steel if like me you cannot afford diamond. They grip with much less pressure than CS-HD. They are soft but not inappropriately so. Also good for very wide bevels on simple steels when other stones start to skate. I don't have a CS-M coarser than 220 because I don't want to deal with a mess like the 120 CS-HD. The 220 CS-M mud is trouble enough at times, so on expensive knives I would start with 320 CS-M or diamond microfinishing film. Were I trying to sharpen for profit again I would get the Matrix stones. Since I am not these will do.
I have 150 & 220 TH stones in 0.125*0.5*6" size. These appear to be a hard version of T4 that doesn't shed grit, and they too act slower/finer than grit number would indicate. I use them by hand for breaking edges.
My newest BORIDE stone is a 220 AM-8 that I profiled to fit serrations. It's a very hard stone that should hold its shape well even under this amount of pressure. (The stock 220 stone that just skates on flat edges actually breaks down fairly quickly when used in serrations.)
Medium stones
I have in the F320 to F400 range, approximately in ascending rank of breakdown: AM-8, T2, TH, AS-9, Orange EDM, Golden Star, CS-HD, CS-M, Sigma Power #700 3F Carbon. As mentioned at the start these all more or less perform as expected for the kind of stone each is, but I'll try to answer any specific questions. Since you asked about the Golden Star: these are very smooth operating stones that feel pleasant to use. They finish finer but on average cut a little slower than the other alumina stones. Their performance seems to depend on the steel a bit more than others (e.g. the unusually consistent 600 Orange EDM, a favorite), sometimes being faster or slower than I would expect from the apparent hardness of the steel alone. Since these appear biased toward finishing I have never tried one coarser than 320.
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