Drewser makes an excellent point.
I can't speak for 86 and later models, but the original 84 and 85's with the Z51's drove and handled like go-karts. They were the first mass production sportscar to pull 1-g lateral. That's why I bought mine.
The Gatorbacks were designed for the car and, with them, it had the best steering and handling (admittedly sacrificing ride and noise) of any car I've driven- because it didn't handle or drive like a car. It drove like a kart.
Sadly, Gatorbacks are no longer available, and not much is in the original 255/50, so if you didn't have the opportunity to drive one with new Gatorbacks, it's not likely you've experienced what the cars can really do.
I have no experience with the GSC, but I can say that neither the SZ50 or Z4 in the stock 255/50 profile begin to approach the Gatorbacks. They both squirmed and wandered, and in the case of the SZ50, it's possible that part of that may be related to the tread width. Or not, that's only a guess.
Again, I'm only talking 255/50 and 84/85 here. Any of the tires may work great on other vettes, and I hope they do.
In my case, though, it's enough to make me consider getting rid of the car, and if anybody's got kumhos or S03's on an 84/85, please post a review.
...and I'm in a Strat phase right now, btw...