Like Troy stated... The best way to go, is to reduce unsprung weight. This would include all turning parts of the drive train. I'm not sure exactly what the ratio is, but it's some thing like ... one pound of unsprung weight = 6 pounds load weight.
So if you could remove 10 lbs from the wheels (2.5 lbs per wheel) that would be the equivalent of taking 60 lbs out of the car or body. For the $$ carbon fiber for weight reduction is very costly. There are carbon fiber hoods for Vettes that cost about $900 and only remove about 12 lbs.
So if you look at the unsprung weight ratio... that would be like losing 2 pounds off the tires, or flywheel, lighter torque converter (for the automatics). Lot more benifits starting with unsprung. What is the weight of the rear seat... or the front seat??? Some one needs to pull these out and get an acurate number.
This guessing stuff is for Ricers... not GTO's.