I was wondering what he meant by "M390 rockwell hardness at 58 HRC?" The rockwell hardness of M390 at 58 HRC is 58 HRC. Would M390 at 58 HRC ever be M390 at 60 HRC?
But to be serious for a minute, if someone wants a tough steel, they should probably look at another steel instead of dropping the hardness below optimal for a steel not meant to be "tough." Why not go for S110V at 47 HRC?
OP, there's a reason a lot of bushcraft knives are made in easy to sharpen steels and there's a reason hunting knives are made of more wear resistant steels. Two different goals. Why not go for something like CPM154 at optimal hardness? Easy to sharpen with mediocre edge retention, better than poor toughness, and pretty corrosion resistant. Or AEBL that's tougher, easier to sharpen, and still quite corrosion resistant?
I want a jackhammer bit made out of Maxamet at 50 HRC. Doesn't make sense.