Saw this in a magazine once as a kid, always stuck in my mind since.
Here are the contenders:
Ferrari F40:
357 kW
577 Nm
3.0l twin turbo V8
1100 kg
Porsche 959:
335 kW
500 Nm
2.8l twin turbo flat 6
1450 kg
Lamborghini Countach 25th Anniversary:
340 kW
501 Nm
5.2l V12
1494 kg
The magazine had an Esprit thrown in as well. Call me biased, but I think it was a bit in over it's head, so I replaced it with the Corvette ZR1:
302 kW
522 Nm
5.7l V8
1590 kq