The lower weight of the LX does nothing for it because everyone knows that body kits make your car go faster. If you have a clean LX coupe, and you want to race a GT with a extended aftermarket Saleen wing and a 5" cowl hood, you better have a stroked out turbo and hope the GT has a stock engine or you don't stand a chance.
No really, my GT is almost a LX now, just the GT nose remains. I always wanted an LX, but both times when buying a Fox, there was no good LX's around. I have all the LX trim stuff. Well, the guy before me put tail pipes on the GT, so they melted part of the back bumper and when he went up his steep driveway it banged up the GT bumper, so I put the LX bumper on. Now the side skirts went, which will require body work and has been quite a chore. Next is the nose. One of the first things I did to my car was take the fog lights off due to the fact I know how much they weigh and the fact that you can't even tell when they are on from the inside anyways. That bracket is heavy, and is located in the absolute worse place it could be on the car besides the wheels.
About the weight differences. I am sure if you had a fully loaded GT, and took a very base model LX, there would be close to a 200lbs difference. Power windows, locks, prem. stereo, ect. Now a convertable GT, now thats where there is some weight!