It depends how much of a liar you are... 3-7bhp at peak, is my generic copout amount, I actually have no idea how much mine got as my "before" dyno run turned out to have an airflow issue because of the Renegade airkit I hadn't, at that point, thrown in the bin. There was a 10bhp difference but no way is that all from the cams.
But, it's not all about the peak, frinstance, mine now doesn't drop off hard after peak, and it's close to the peak for far longer. I'd actually sooner have 65bhp and my power curve, than 75bhp and a standard curve, for the ridability. Though that's not all the cams either.
There's another option I forgot to mention, which is using another set of curvy cams in the intake side. I think either Carsick or TSM has this, with an old set of mine
Not quite as good, but still probably 3-4 bhp and it should help the fall-off past peak as well. Cheaper, though, in fact it's possible I have a pair of curvy cams in the garage, if so they'd be for sale, £50
