I am used to sharpening ZDP, S30V, CPM D2, VG-10, ect and find CPM M4 (as done by Tom Krein) to take an incredible edge whether it be by DMT, Spyderco ceramics, or Shapton Glasstones. It sharpens easily for me and even at coarser grits starts pushcutting extremely well. When finished off on .05 micron lapping film the sharpness is stunning. Then again, I just sharpened my ZDP-189 Stretch 2 the other night and am marveling it sharpness wise. I just remember when sharpening my Krein M4 knife side by side with other steels it was the pretty always the sharpest.