Honda/ Acura HSC is a dark horse, as well as a frightenly fast car when dialled in.
I've said goodbye to many CSL's and LFA's in a HSC, and before you say it - no, they weren't being driving by numpties, they were drivien by very good drivers who know setups well.
An M5 '08 can also take out a CSL at tracks like Monza and La Sarthe - been there and done that too.
The BMW CSL's and GTR's have awesome all round ability, they are truely brilliant cars (possibly some of the best all rounders in the game), but oh so boring, every race, there's just so many of them....show some originality guys!
ALOT of other cars like the Shelby Series 1, Oullim Spirra, RUF RGT and Lotus Evora can be crazy fast too, once dialled in.
There's so many to choose from, why be a sheep when you can be the shepherd.
As for undesteering a GTR - no way, those cars turn on a dime once setup, you don't need ballast either - it's all in the braking sensitivity on the diff (high front, low rear), rear toe (change from + to -), brakes (rear higher than front) and ride height (3-10 mm lower at back then front).
Easy peasy...that'll make any 4wd turn in like a MR, all mine do.
Check out the roll bar thread in the tuning section, that's VERY useful, also consider the "indirect tuning" approach. If the front is understeering, you don't ALWAYS have to change something at the front, loosen the back and the front will turn more. Same with front and an oversteer-y car, change the front and it can help the back. BUT only go via the "indirect tuning" method when all attempts at the direct method have failed.