The Vincent Comet, which is often derided and described as 'half a Vincent' is actually a very nice bike, and it would be much fairer to compare it with contemporary 500's.
Brian Chapman really liked them, so much so that he built 'Mighty Mouse' (pictured above) and proceeded to smash records with it in the 70's. The bike's fastest time for a standing start 1/4 mile was 8.81 seconds. That's about a second quicker than a current Suzuki GSXR1000 or Ducati 1098R, and remember, this was a 500cc single cylinder engine which was 20 years old at the time and designed in the 1940's.
It was superseded by 'Super Mouse', with a full on Vincent V twin. This gained Brian a further 0.56 of a second on the quarter mile making it the fastest British single engined bike, keeping the Vincent flag flying against the multi-engined superbikes of John Hobbs and Henk Vink.