There will be some interesting opinions on this. Some guys grind only hardened blanks so they can address any warps. Some guys will take it 75% to 120 or 240 grit and then finish after hardening.
Some guys, like me, take blades nearly all the way and to a 400 or finer finish. If it warps, I make a new one if I can't grind out the warp. Most of the SS warps I have seen are from heat treat foil sucking up to the blade like a vacuum. I now sprinkle talc powder on every blade to avoid that. Peter's uses gas quench and neutral environment ovens so you don't have to worry about the foil part of it.
What I do know is Elmax is hard to finish when hardened. Hard.
Getting scratches out can be a bugger and over heating while getting those scratches out can be an issue. Grind a pass, dunk, repeat. Other super steels can also be tough to finish like S35Vn, CPM20Cv, M390 come to mind so those I take to final finish and then it's much easier to clean up any heat treat patina.
