I'm running a 335i sport with H&R Sports and I've been to two different Autocross events so far.
My first one was setup on a gokart track and the car handled amazing. I was doing around the same times as Mazda Miata's and an 2011 M3 ran 55.0 and I did 55.7 so pretty close.
2nd run was a bit more difficult at an AutoX that was setup in a parking lot but it was last Sunday where Hurricane Sandy had left the area well very sandy. They brought in a street sweeper but did not help me as I was sliding around the place a lot. My times weren't too bad but the all wheel drives owned that day for sure. I am not sure about the results as yet because it hasn't been posted as yet.