I voted "other". I put a Blue Flame high-mount Titanium exhaust on my bike and absolutely love it. The quality is top notch, the sound is awesome, and performance is excellent. I don't know if it added power or not, because the difference is so minimal. However, it did free up the motor. It revs easier, drops between shifts easier, it smoothed out the shifts, and the bike just seems to be more responsive.
I know the pipe is available for the F4i and Jessah had one and was very happy with it. Here's a pic of what mine looks like. They have a couple different models in the evo series - including different finishes (polished, carbon, Ti) and dual and single port exit. Also, all of the pipes in the evo series come with removable silencers, very nice feature.