The 520 to me has shelf space all its own-- people gripe about shredding, hate the chalkiness etc, but to me it's about the perfect hard-use knife, avail in both 154CM and M4 (sec'y mkt for M4). It's a comfy fit for leverage and the grip is superb, gloves or bare.
I don't get too bent out of shape regards steel choices. To me M4 can't be beat but I'm perfectly happy w/ 154CM too-- they're equally useful when sharpened, M4 just holds the edge longer is all. While I've always preferred tool steels I've come to appreciate the maintenance-free aspect of stainlesses as well. Were I to be using a knife all day I of course would want the edgeholding of M4, but for occasional (NORMAL in other words) use, any steel serves.
Grips are great, but for sustained use just aren't as comfy, for me anyway.
I appreciate your help !