Bear with me. I could ramble here.

the differences are a few but crucial. WSB allow use of non stock cranks, pistons, rods, cams with lift and duration while bsb you have to use the (original)road spec items and cams are only allowed duration not lift. There may be other differences but I am not the expert. A very good friend of mine is in the paddock and gave me the inside track that on their bike these mods are good for 20 extra horses on the dyno.
Shakey's bike is already homologated with super trick internals so these changes to his bike would not have made as big a difference. Also, I understand his bikes are handbuilt in the factory. Any wonder he is runing away with bsb?
One of the reasons this was introduced this year was to make it cheaper. Again, my source informs me that they didn't need any engine rebuilds last year but will have needed 4 this season.....you guessed it, its made it more expensive.
Back to the question in hand. Tyres, chassis, conditions, and not forgetting rider talent all make a diference to times but i'll wager 20 horses don't half help.

btw, feel free to add to this as i'm sure there are those out there with more knowledge than me....and like any good journo, I am not going to reveal my source!