Just had new T30's (not GT) installed on my ST1100 last night. The front is noisier than the old Avon ST22 (date code 1992, 550 miles) that was removed. At the rear an old Dunlop ArrowMax was replaced (date code 2003, 550 miles).
I've got a total of 96 miles on them so far.
My initial impression is that the T30 rolls over things like tar crack patch and asphalt hole patches better. The Avon tended to bounce to the side when I hit tar crack patches and had a little bit of deflection on some asphalt hole patches. I've been riding pretty carefully so far, but I did have one slip at the rear on the way home crossing some white road paint in the light rain I was caught in on the way home from the dealer.
Other than the noise the tires feel good and ride nice. I've read some very positive reviews on this tire, and I'm hoping we all see good performance as our tires wear. I'll be interested in see what people think as their tires wear over time.
Edit: After putting about 100 miles on the T30's I checked the pressures and found both front and rear at about 30psi. I added air to bring both up to the more correct 36/42 psi and took a ride. Tires are a lot quieter now, but still a bit of sound on grooved concrete.