i gotta say, i had an f7 for awhile and i didn't feel that it was an all around increase in power. the top end had a lot of peak, but it came on suddenly. it didn't really start getting into it's band till a little further on in the revs. not a lot of low end power (which is great for straightaways, but not so much for the trails....at least not the kinda trails that i encounter).
if you're goin w/ a bbk, i'd say get the big bore shearer or the vitos judgin from what i've heard, but not the trail shearer for the stock cylinder.
for trail riding, i can't say enough how much the trail shearer kicks ass. it's just balls from the bottom up. maybe not as much peak power, but def a LOT more usable power since the band is so much wider and stronger.
of course the proper port and polish and head work def will really bring the motor alive. and i always recommend kennedy for that work!