While driving to his home David Letterman was ticketed for driving 205mi/h on a highway with a speed limit of 55mi/his this impossible, possible but very unlikely, possible and likely? why?
I would rate this as possible but very unlikely.
(1) Most street legal cars are incapable of reaching these speeds. The 2013 Ford Mustang Shelby GT500 has a top speed of around 200mph. There are street legal cars that reach speeds of up to 250mph
(2) A road marked at 55mph is different from a road marked at 65mph. If this was a 4 lane divided highway, it would probably be marked at 65mph (except near large cities). A 55 mph road might have only two lanes or significant curves/hills. Note that a Formula 1 Gran Prix car is built for turns and can reach speeds in excess of 230 mph, but they are not street legal.
(3) If this had been Jay Leno, I would change to possible but only a little unlikely, as he is known for his love of cars and his large collection of cars.