This list does not have the fastest, but ones I find to be a lot of fun. Besides, folks have already hit the obvious rockets in the range. A well set up Rx7 is hard to beat.
Personal fav is my Mustang tuned to approximate my personal ride, 2012 5.0 with Brembo package. Actually sits a bit lower at 492PP. Runs 7:57 laps on sports hard... Think eventually I will get it into the 40's. Probably not the best for races but a blast to drive after much tweaking.
Maxed out Golf R is close to 500, maybe a bit over?. Easy car to get around especially with a torque splitter to bias it to the rear. TTS is similar and faster. Without trying to hard I was cracking 8 minutes with the golf. Haven't run a 500 spec with the TTS.
Another less. common option is the infinity g35. 500 PP gives some decent room to spiff it up. I use it as a stand in for a left hand drive 350z. It has almost identical handling if you get the weight and weight distro matched.
A tuned M3 CSL is a very nice ring ride. Wish it was a premium as I prefer the cockpit view. Probably be my weapon of choice for online races.
The Camaro SS is a very solid ride. Sports hard, stock with an oil change I have run 8:0x laps pretty consistently. Wouldn't take much to drop its times considerably but cannot remember its stock PP.