Losing weight from the rotating assembly will always mean it takes less hp to get it spinning. The problem is the reduction in driveability. If you're a bolt-on type of person at the moment, a light weight flywheel is far beyond what you're looking for, and is not a cheap and simple mod, and will NOT give you lots of free power. You'd be better off turning your boost up a couple psi.
If you're a serious engine builder after every free hp, then go with a lightened flywheel.
I've run light weight flywheels and lightened stock flywheels. If you go too light, you kill the driveability and it's not fun to drive anywhere but on a track.
Do you go faster? Yes... a very small bit. Is it worth it? Not always. I probably won't ever put a lightened flywheel on another of my daily drivers.
If I remember correctly, the stock flywheel weighs 18 pounds.
I can tell you from experiece that #1. A light weight flywheel on a supra does make the car feel a little more responsive at low RPM. #2. It does not effect drivability in any negative ways. #3. It won't make launching the car at the track any harder. #4. It will weld its self to a HPF clutch.
anyway, i have an rps 11lbs. flywheel on my supra and it is, or actually was my DD till it started knocking... but anyway, it just feels more responsive and i dont see how it would affect drivability. maybe its because i first learned how to drive stick with this car, but i actually like driving with a lightened flywheel. if anything, it just made me downshift easier with it being so responsive.
i drive my brother's e46 330i from time to time and i have trouble shifting smoothly since i was so used to the feel of a light weight flywheel