I have Aaen pipes on my 4/6, it's been ported and has shaved heads. When I got it, it was clutched to run 8800 RPM. Yesterday I pulled some weight off from the primary ramps. It would then run 9000 RPM, it sounded a lot better and was noticeably faster. I don't have a dyno, but at 8800 RPM it only would run 70MPH, at 9000 it hit 80 with ease (both runs done on a snow covered plowed road). I'm looking forward to running it at 9250 to see the results.