Just to add about the Street legal 911 GT1:
(From Wikipedia
http://en.wikipedia.org/wiki/Porsche_911_GT1)
Street-legal version
Regulations for the GT1 category stipulated that to be eligible, a total of 25 cars must be built for road use. Porsche developed a fully road-legal version of the GT1 and delivered one in early 1996 to the German government for compliance testing, which it passed. The engine had to be slightly de-tuned to meet European emissions laws, although its 544 PS (400 kW) and dry weight of 1100 kg (2425 lb) proved to be more than adequate; the vehicle could accelerate to 100 km/h (62 mph) from a standstill in 3.5 seconds on its way to a top speed of 310 km/h (193 mph).