My 710HS (the M2 model) is one of my 2 all-time favorite folders. I'm very happy with the M2 steel. My subjective impression is that the edge lasts longer than the ones on several S30V knives I own. I take care of my knives, and I don't live in a swamp or a jungle, so rust isn't an issue for me. The M2 takes a really fine edge that will split hairs with a quick touchup.
Sharpening difficulties with M2 can be minimized by reprofiling the edge to 30 degrees inclusive (or thinner) on a Sharpmaker (takes hours), Edge Pro, or freehand, and then maintaining the edge with a microbevel using the 40 degree inclusive setting on a Sharpmaker. If you reprofile, it takes only a few strokes on the fine or ultrafine rods to bring the edge back to the hair-splitting level of sharpness.
If you can find a 710HS in M2 for a reasonable price, by all means get it. They're beginning to get scarce. The D2 version is now available at various online dealers.
I've never used the newer D2 version, but I'm sure that's a great knife too. I have several D2 knives and they perform well, although I can't say that the edge I get on them is as fine as I get with the M2, at least not with the methods I use. If, God forbid, my 2 710HS knives get lost, broken or stolen, I would likely get one in D2.