We did organise already 3-rd time top speed race here and I post the results, because it's always good to know your opposition.
Race distance was 1 mile from standing start and speed was measured exactly at finish line. I would say don't mess w. 996 Turbo. Particular car was tiptronic and therefore slower than manual. As I was organiser I hadn't time to run by myself, so no comparison with our cars, I guess you would need 350-380 rwhp to run 250 kmh.
http://www.tqhq.ee/omc/
