This whole topic is such a bag of worms - but I don't think any of us can resist!
IMHO (I've learnt a new acronym) power is nothing without the skill to exploit it:
eg., the higher the skill, the better the rider is able to exploit small bhp differences - so at MotoGP / WSB level a few bhp can be important BUT at lower skill levels the rider is the limiting factor and it takes a much larger bhp difference to significantly affect lap times.
My lap times arround Snetterton and Cadwell on a 162bhp Probike and a 112bhp 600 are virtually the same. Tellingly, I was marginally quicker on the 600; I believe because it takes more skill to USE the probikes 162bhp and I don't have that skill.
I do know that the most effective way to improve my lap times is to improve my time through the corners and I am certain that working on this aspect (mostly skill but perhaps some bike set-up) will give me bigger improvements than an extra 5 - 10 bhp.
Everyone seems to be hung up on BHP what about the torque advantage that the bigbore bikes have. also we have run 620ie back to back with a 750 carb monster with the same rider the 750 was 1.5 seconds a lap faster at rockingham. As a side i bought a complete 620 motor with loom and all injection yesterday fo £550 (6000 miles)so they are out there Butch