No gap whatsoever, to me.
The sport is the deal, and the GT is taxed with accessories that can easily be installed or bettered by using aftermarket stuff.
Headlights - HID's or at least better bulbs. No, you won't have the adjustment dial in the car, but this car doesn't have an issue with headlight pointing...the suspension is not soft at all.
Taillights - Take em or leave em
Trip computer - Can be turned on in sport models
BOSE - Puleeze. The stock stuff can burn in hell. The stock head unit on the BOSE is better, though. It outputs a more flat signal then the stock Sport head unit, and thus is a better head unit to start with if you are going to build a custom system with the stock HU (I can recommend that you do this...it works perfectly if done correctly.) However whether you are running the Sport head unit or the GT's Bose unit, you'll find a processor that can integrate the signals to aftermarket equipment like amps to be very useful and important to great sound quality. This makes getting the BOSE head unit a wash, since you can easily compensate for it with a processor.
NAV option - Again, take it or leave it...for the price I'd leave it and buy a Tom-Tom or something PLUS have enough money to afford to actually go somewhere.
Leather - Well, I have the stock cloth seats, and they are fine. Leather in just certain places seems to be a bad idea to me. Especially in the places they put it. That outside edge of the seat gets a lot of abuse, and even the cloth is showing a bit of wear. I can only imagine how much the leather would show.