The most performing car(s) you guys have ever driven in a game.

[OPT1MUS]

(Also special tuned versions or prototypes)
Mind that I'm not talking only about horsepower: mere power is useless if it isn't supported by a valid setup, which implies stability, handling, etc.
As of today, I find that 2 cars are still unrivaled, for me:

The Warrior PTO E/2 (from the first Need for Speed)

A real monster, no tuning of any kind, original as it is. Incredible grip and maneuverability, combined with an absurd speed: to this day, its top speed is still unknown to me; I managed to reach 530 Km/h (about 330 MPH) but it could still go further.

Dodge Concept (from Gran Turismo 1)

Already formidable as it is, just a little tuning and with a little setup it becomes a rocket capable of accelerating in the blink of an eye and quickly exceeding 300 km/h while remaining glued to the ground, able of tackling turns as if they were straights. Thanks to it I was able to make unrepeatable track records.

So... what are yours???

 

[Zerpina]

The El Niño from NFS 3: Hot Pursuit...
that thing was an absolute monster. Perfect turning.
I think it topped out at 220 to 250 M.P.H. I don't remember.
I know it was the fastest car in the game.
Cue *Sonic - Fastest Thing Alive* music

 

[Cu1tur3D_Gam3R]

This car, the 2002 Cadillac Cien concept in Gran Turismo 4, when strip down the weight, tune up the engine & add a spoiler, it is a supercar destroyer & then some. Hell, this & the Opera S2000 were busted when you utilized them to max.

 

[bjork]

I suppose it has to be this, though I only encountered this at one arcade. From what I understand, it was the most accurate recreation of a supercar at the time.

 

[Nelson2001]

For me it would be the Audi R8 Race Car (2001) from Gran Turismo 4 (2004-05) which is a hyper racing car that has a slightly more stable handling compared to the other hyper racing cars that I had used in the game (such as the Nissan R92CP Race Car (1992) and the Mazda 787B Race Car (1991)) and also reaches up to 400 Km/h but with customization adjustments in the changes it can reach up to 416, 417 or 418 Km/h but if it is with nitrous (Although it runs out quite quickly) it reaches up to 446, 447 or 448 Km/h.

 

[Nebulon_Galaxy]

The 1969 Buick Electra

 

[middler]

I have 2 standout cars The Mitsubishi GTO Twinturbo from Gran Turismo 1

fully tuned nothing else could beat it

And then later on from GT4 the Red Bull X2010 Prototype

This car was a freaking cheat code.