I believe the RW power to total weight ratio has a direct, predictable influence on MPH numbers, give or take some depending on aero, etc. The weight of certain reciprocating components is part of the total weight, but the influence of changes of those components on ET is hard to predict.

A lighter reciprocating assembly in the engine or transmission will accelerate quicker. But wheels are not being accelerated to thousands of RPMs. However, taking 40 or 50 pounds out of the wheels is 40 or 50 pounds out of the total weight and the unsprung weight which effects suspension efficiency. 50 pounds should make a noticeable difference, regardless where it is removed from. It may be more of a difference coming out of the wheels.