I believe you win the Kusabi from the Roadster Race A-Spec and you can buy the RX8 new.
Not sure what everyone is running for the second set of Seasonal Time Trials though.
Ive only tried it once, first time I have driven the Mustang (what a rubbish car) and I got silver and .3 of a second behind first. I think a second attempt with some suspension tuning a gold would be easy.