sram shifter pull twice as much cable so in theory, an x mm cable stretch/inaccuracy, is less of a percent of a gear shift.
from my own personal experience:
I've replaced my shimano on my mtb with sram (x5 mech) and the mech feels chunkier and better quality. And it now works, as opposed to having shifting problems with shimano. Only thing not quite as good is sram shifters dont' seem quite as ergonomic, but I'll probably not think that when i'm more used to the different shifting action.
fwiw I think the shimano shifting problem that i had was due to the shifter, but i couldn't be bothered to take it apart and rebuild it esp. when it might not have been that.