My personal experience: Bought stock bike, rode it for a while, noticed significant drop in power between 4,000 and 7,000 RPM. Installed full exhaust, K&N air filter, and PCIII supposedly tuned for that motor/exhaust combination. Compared to published stock ratings, the overall HP increase was minimal. The biggest advantage though, was that the big dip in power in the middle of the RPM range was eliminated. It pulls the entire way through the RPM range now. I believe there may have been a slight loss in fuel mileage, but I can't remember exactly what it was previously, I do however get 39 MPG at the moment, 45,000 miles later. My main concern is that I believe it has been running too lean. It backfires upon throttle release. At first, I was lead to believe it was because the engine was running too rich and the backfire was caused by excess fuel being burned off. I have later heard from two other individuals that it is more likely that it is too lean. Any opinions?