One issue you'd hit is that Rosetta is going to do fairly linear translation, and isn't going to improve calling conventions to the native one (in practice not

One issue you'd hit is that Rosetta is going to do fairly linear translation, and isn't going to improve calling conventions to the native one (in practice not terrible as x86_64 mercifully has enough registers for the all arguments in the general case). In a sense if you were to go through the hand assembly one at a time and do 1:1 substitution with ARMv8 equivalent you'd probably be able to do a bit better, just because you don't have to consider behaviour of generic x86 code.