Drop it like it's Hot, I think I used a slightly modified S7 with front & wing upgrades. I believe I had more power & torque, so as long as I managed wheel spin off the start and took advantage of the AI braking early for each other early on, I got out in front easy enough.
For High Noon, I used the same Audi you did. I was able to grab 1st the first two times and saved the dirt track for last b/c the AI just seems to adhere to perfect racing lines without any issue. I came 4th, but was still barely ahead in points to win the championship.