It's just the shift gates that are tighter. the gearing is the same.
The reason you see so many variances in the time slips is mostly due to how high in the rpm's people land after shifting. I've seen people land as low as 5500 rpms and others land at 6400 rpms like you're supposed to. this can cause a variance of .5 seconds or more. It's basically all about who is driving. A great way to measure 2 drivers in a gts is to look at the 330' marker. with equal 60' times, he 330' marker will tell you who was shifting the 1-2 shift better