Just what is the fastest car in the world? Over the last few days, no one seems especially sure anymore. The Bugatti Veyron Super Sport had held that record since 2010, but it was revoked over the weekend. Now the official title has reverted to the SSC Ultimate Aero — and SSC says their forthcoming Tuatra will be even better. But Hennessey Performance says that the Venom GT is faster still, and don't forget the Koenigsegg Agera R. What gives?