I have to say that my fastest car that I had in top speed was in the Jaguar XJ220. I got it up to, according to the last post on it, to 268 MPH.
My fastest 0-60 time was in the Mitsubishi Evolution FQ-330 at 1.9 s, same with 0-100 at 3.4 s.
I do not have the ratios or anything on me, but it is essential to find the correct ratios, because the games ratios can be crap sometimes.