Coupes are lighter...
If you take a GT hatch and a LX hatch, with the same options/rims/etc, the difference is the ground effects. They weigh between 30-50lbs max (I've had them off before).
The coupe is lighter because it doesn't have the heavy 70lb hatch/window. In its place it has a light-weight trunk lid and rear window.
After owning a 87GT hatch, a 92LX hatch, and a 93 coupe, I truly believe that people make way too big a deal when it comes to those "dramatic" weight differences. My fully loaded 87GT T-5 car weighed the same as my fully loaded 92LX hatch AOD, 3250lbs. The tranny offset the weight of the ground effects...
You take any of these given factors, it still more often than not will come down to the driver in a race, rather than if you have ground effects, or a hatchback. Those are just excuses that inexperienced drivers make themselves feel better with...
I will admit, that you take a Fox vert, fully loaded with AC, and it will weight a few hundred pounds more than a no option, no AC, T5, fox coupe...