Lamborghini Gallardo. 5.0l V10 - 500bhp. That's the largest engined most powerful car I have driven, not much between the 143bhp 1.8 4 pot that was the most powerful car I have owned.
Vauxhall VXR8 6.2 litre and about 520 bhp I think. It was at a Vauxhall track day at a damp and greasy Thruxton and the Corsa VXRs could easily catch it because the TC wouldn't let any power go to the wheels.