I feel like some credit needs to be given to the Virtua-Lemans guys, the tracks they do for rFactor really are top notch. Mid-Ohio, Lemans, etc., are all awesome tracks to drive the Vette on. I can't use the Historic-X mod, or whatever it's called, as it sounds like you need a GPL disc, which I don't have.
That being said, even with the good mods in rFactor, the back of every car I've tried just acts like it's in another dimension most of the time. I can't go more than 30mph around T1 at Monaco without spinning. I can't save slides 1 degree past the limit. Worst of all, I CAN save slides by steering the wrong direction. Car straightens right out...
I didn't write it off immediately either, I've had it installed for over a year. I've tried every combo of settings, every value in Real Feel tweaked over and over, and nothing changes the fact that the ISI engine sucks, and guys like Niels have done their best with it, but they can only do so much...
Edit: And what's up with night racing being unplayable with more than a few cars? I can get 200+fps during the day, but a field full of headlights at night brings my system to a crawl.