The S4 is an extremely capable car and considering its weight handles itself quite well on the track with the sport differential.
Hell for less than the price of my exhaust on my M3 look at what this guy dyno'd on his S4...
The track day I brought it too I had. I problem passing e90 model M3's with them having better tires and brakes as I was totally bone stock on the S4 with very crappy tires.
With my S-tronic tranny I would laugh at a convertible M3 if it tried to race me from a stop.
P.S. to the guy saying his convertible M is better because he can take the top down is a win ...lol that made me laugh.
Both cars are excellent cars I just find it funny with all the Audi haters and BMW haters I see on both forums.
I personally don't give a crap about brand as long as I enjoy the car. I'm actually starting to love American cars more now (always loved the Z06) like the mustang boss 302.