[Bill Edgeworth]

I don’t think you can really make a blanket comparison between steel and aluminum drive shafts. Beneficial to some not to others, there is a lot of things to consider when swapping them out and seldom are the new and old physically comparable. One would first think that if its lighter it will take less energy to accelerate… well not necessarily if you take a small diameter steel shaft and replace it with a lighter large diameter shaft.
Here is an example
7000 rpm a 3” shaft will have a surface speed of 5498 feet per minute
7000 rpm a 4” shaft will have a surface speed of 7330 feet per minute a 33% higher speed
Using basic physics equations like Ke=1/2mv^2 if they weigh the same and most of the mass is in the tube not the end yokes the 4 inch shaft will take roughly 78% more energy to accelerate to 7000 rpm.
If you do all the math the 4” shaft would have to be about 40% lighter to take the same amount of energy to accelerate as the 3” shaft.
What this exercise shows is that most comparisons are apples to oranges you probably won’t see any gains unless you are replacing your current shaft with something lighter and the same or smaller diameter.
And this is without taking into consideration what’s going on in the rest of the car.

For something as simple as a drive shaft there is no simple answer.