Jamz wrote:
But how can you get away with it, anyway?
When I had mine bored out the difference was massive! I would have thought it would stick out like a sore thumb especially driving out of the corners?

Well, mostly they're done by people who can't believe that the front runners are actually faster riders than them and therefore must be cheating, then find that they still can't beat them
On a race engine they don't give that much extra top end bhp, maybe 2 bhp, but can give as much as 10 bhp midrange along with the added torque. As you say it shows coming out of the corners, that speed is then carried down the srtaights. But, a good rider will just have to work the legal engine harder to get out of the corner better, ie, use the power at higher revs. In other words the 440 bikes are 'easier' to ride fast!