The Ariel Atom is quick and handles pretty damn good...when it's working...but I don't recall any statistics to confirm that it's the "fastest".
I've been on the track with Atoms and according to those two owners, they had to do a lot of modifications to even keep the damn thing running half decent for a few laps without breaking...exhaust headers constantly breaking, things melting...not all that well developed from the factory...maybe they eventually corrected it, I'm not sure. This was one from last August at NJMP:
