My theory is it will just weigh less. I just built my new bike with a LX drivetrain and XT shifters and after all adjustments it works perfect. How can something do more than you ask it to? If my bike weights a few ounces more, BFD. Untill I have 10% bodyfat there is no sense in caring about a few onces on a bike.
I would rather spend the cost differences on better tires, handlebar streamers, or burritos.
To answer the OP: Sram is for hippies and troublemakers. Always keep an eye on those hooligans.