I say 2013 S6, if you ever considered an M5, I think this could be the way to go, it's cheaper(same price as a well equipped M3), it has 480hp stock but goes up to 560hp/600ft-lbs(M5 beater
) with just the APR tune which in my opinion is a realiable mod, Audis FI engines have always been pretty much bulletproof!
Also IMO the S6 interior looks a lot better then the pricier M5 and it has AWD which is almost a must when you deal with that much torque. Unless you're surching for a car to bring to the track, I think there's no better deal than the S6, a germain luxury/sports car in the low-mid 11s for around 70k is a hell of a bargain!!
I know I'll consider one of these when it'll be time to change my M3!
Good luck with your purchase, shopping for cars is so much fun!!
if you're not already familiar with the car, have fun with this