I've only used the Spec-V in the car battle, and it stuck like glue, which is rather suprising at 150+. I've been playing around with my porsche GT2 and cayman S the most. I did end up buying a Lotus Exige for tighter tracks that are hard for the porshe to do since they get a little back end happy. I will probably end up selling the Cayman S so I'll have enough for the Zonda R.
Also, endurance races are awesome, and actually make you feel like an actual race.