I'd say for 10th off road it's pretty negligible, if you need more power drop turns, there isn't a great need to spend all that much, in touring cars, yes, money wins races, but where the speed of the car is traction limited not power limited it's pretty much all skill imo. Neil Cragg for example generally seems to use much less powerful motors than most others (from what i've seen anyway, feel free to correct me here
) ofc they're all top end brushless systems etc, but that's reliability, not making him go faster. Only thing that would maybe make a difference is top end batteries making the voltage more consistent over a race, or where it's allowed, lipo dropping weight and adding power (Doughtys car at CML 2 weeks ago sunday was a rocket, and it was damp
)