I remember during the first months of the original Halo release on PC, it allowed you to play cross-platform. It was quickly stopped though. I remember playing it vs. console gamers and winning every match with at least a 20piont gap. I was accused of hacking several times.
I am not trying to say that I am a superb FPS gamer, as I get my ass whooped on the right server. I am just using this as a small way to help illustrate my belief of KB+M>Console Controller.
(I do also understand that this may not be a fully fair comparison since at this time FPS on console was still a mostly new concept.[golden eye excluded])