I replaced my gtp with an 04 CTS V a few months ago. I test drove an 09 G8 GT but I wanted a 6 speed so I went with the v.
I really like the car so far. As long as you dont launch the car every time you accelerate the rear end will be fine. If you look at one make sure the motor/ trans mounts are good and the rear end isn't whining or clunking. My rear end whines a little bit with only 35k miles on the car. the 6 lug wheels suck too.
I hear horror story about 06 or 07-10ish Audi A4/S4's, they are nice cars but seem to have an issue with the direct injection system on some and its very costly. Other things to consider with an Audi is anything maintence wise on the motor, like timing belts and such. Talking big dollars for repairs on those.
evo 8?