The R35 is a beast, but it's also a GTR... boring, there's only 20 other GTR's in the game.
You can't go wrong with a BMW.
The R8 Team Playstation is a little faster, but good luck finding it. The 458 at 600 PP is just a joke...
My best recommendation is the RX-7 TC. If ya tune it right, it's almost unbeatable in the 600 to 625 pp range. ( kept up with the 2J, but still lost. only by 3 seconds after 5 laps. Daytona Road Course)
Here's your base setup, Put everything on it. install the MID RANGE turbo. This car is unstable with default suspension settings, so you will have to tune that out. A good tune track is Spa, the chicane before the first long straight will tell you if your settings are right or not. If they are wrong, you spin. If they are right, you should be able to take the corner at full throttle.
The gearing should be kept short. Shift at 8K to stay inside the max power range, you should drop to around 6k with each upshift. The rest of my settings are top secret, but it's all in the drivers preferance. Fine tune it to fit your style and you should have an unbeatable car.
(hint) keep it BELOW 630 pp. It can be a handfull at it's max power (641 PP
)
The mid range turbo will give the best acceleration, especially with TCS turned off. Takes off as fast as a 4WD. The Stage 3 turbo WILL lag out on ya, so stick with the mid range setup.