Actually, 58-59, not 57.
On a hard use knife, toughness is an issue. S30V should be tougher than BG42 at the same hardness, so it is suprizing that Reeves dropped down in hardness slightly. But from what I've heard from owners of S30V Sebenzas, there is no problem with edge holding at 58-59. The blade must be super tough at that hardness.