While almost anything faster than a GT3 is above my pay grade, it's hard to resist the Porsche 919 hybrid; the fastest car I've encountered in AC thus far (not counting fantasy vehicles like a 2525 landspeeder). And there's only one place to see if you're as good as you think you are, and that's the Nordschleife. Yes, the 919 transports you straight to Heisenberg territory: time slows down, circles go all elliptical and straight lines shimmer and shake like an overstressed zip line...
Porsche 919 Hybrid @ the Nordschleife
Porsche 919 Hybrid @ the Nordschleife