Have a look using the search bar, been talk of plenty.
Its not just a case of how big you can go, but how it effects turn in etc of the bike, the smaller rubber on our bikes is pretty optimum, with 140's giving a small benefit. Some have also said that going larger than 140 can lessen the effective turn in, making the bike less 'flickable'. This may only be noticeable to someone who knows how to push the bike to the limits.
Felix