You might also want to look at lightening some parts, mainly the flywheel and clutch. Won't give you anymore power per say, but it will get you into your powerband quicker. I have had a nichols flywheel on my S4 for a couple of months and I'm happy with it. I only rode the bike a few times before I swapped the flywheel for the lighter one, so I really don't remember how it rode with the stock one. I threw a yoyodyne lightweight clutch kit on last night and I'm also very happy with it. Much quieter than the stock setup and tons lighter. Very impressed. It seems like the clutch kit had more effect than the flywheel did. Which probably should be the case since I think the stock clutch setup weighs more than the stock flywheel. Flywheel was around $200 (+ $50 for the jamnuts) and the clutch kit was $600 (+ $150 for barnet alum. plates).