I'd take the Zonda C12 Convert, only something like 14 are being made. Italian, Fast, Expensive, Exclusive...what else do you need?
Jeff-
The CCR is faster then the 8...but neither were officially tested. The official (FIA sanctioned and approved) top speed holder is the Bugatti Veyron, a little over 400 km/p, or about 252 mph. Besting the previous record holder, the McLaren F1, by 12 mph. Rumour has it that on the dyno, the Veyron showed a top speed of 260+, amazing what air drag can do to kill your top speed.
There are lots of cars that claim to be the fastest (cough Koenigsegg, Saleen cough), but those numbers, for the most part, are estimates or private test results, which aren't official by any means.