I would worry about red fading, not because of any experience, but red generally tends to fade more than other colors. A vert will increase sun exposure, and the leather interior is a mix of leather & vinyl so the fading will probably not be uniform IMO.
Do you leave your top down all the time???? I traded in a '91 RX7 Convertable (I bought it new) on my new '05 GT Coupe (w/Red Leather), and really did not have any problems with fading. Always use a good quality leather protector (Lexol, McGuires, Mothers, etc...) with a UV protectant on it. When parked, put your top up. I too will be curious as to how the leather will hold up over time, since I intend to keep my GT for a long time. But remember, eventually it will fade some....just take care of it. If you can, garage it....that will help the interior and the exterior. Use a good quality car cover. If you do not plan to tine the window, you can use a clear tint that has a UV protectant built in. Also, always leave your window up when parked, even in your garage. It will help keep the leather from drying out as much.
I have an 05 Redfire GT vert with the red leather and interior upgrade package. Definitely happy with the choice. I think the red and black go great together. Looks especially good with the top down.
As for long term durability, I agree with the other posts....if you take reasonable care of it, it should hold up fairly well.