I had an A4 2.8 quattro on 18x8.5 wheels. It was a nice zippy canyon cruiser. Had a lot of fun pushing the limits of the quattro system. While I do miss the tight sport suspension and pushing the limits of the tires through the turns, I had the car for over 6 years. I knew every ounce of what it could and couldnt handle. I have yet to explore those limits with my 300c yet on the turns. I am still gaining confidence through the turns, and learning shift points etc. Its the learning process of a new car I guess. I'd like to take it to a parking lot sometime soon and reach those limits, so I know what the car can and cannot do. I am not used to RWD any more, so the feeling is a bit unnerving to a AWD driver. I don't think you would be dissapointed however. It takes a while to get used to any new car.
For what its worth, I took the 300c on a canyon run up topanga canyon in malibu, which is known for its severe twists and turns. I was pushing the limits slightly, and my brother in law was getting sick to his stomach. Not a single squeal from the tires.I love my car.
Wait until you get an offer you like, or a buyer you like. I found a buyer I liked, and was willing to negotiate because it would be less of a hassle in the long run. Good clean honest deal...