I have cars for every level (for Pro tourney), but I still pretty much just race the Lambo now, lol. I guess when I get bored, I'll try mastering another car. Today I played enough to move my lambo level 7 rank from 3000+ to 20, lol.
Before they went live, I was in the top 10 on the Beta they had. If you are looking for tips, I suggest you troll their Facebook page for any tips others may post. Some people are nice enough (stupid?) to post their tunes for others to use.
My current lambo tune I got that way! I'm only about 0.015 from the fasted lambo times I've come across. Not bad.
If you have any tips for the Venom, please let me know. I'll put some time into that car probably next week. I have 2.5 mill to dump into my Venom now for more upgrades. Mine is already a level 10 I believe.