Im new to this forum stuff, knida, hit enter and off the post went. Anyways, the bike struggled going up hills, downshifting a lot, I read that this was a common complaint. I ride in Southern Lancaster County PA, not real bad hills but enough, up and down constantly. I noticed a substantail improvement going up hills, not earth shattering but definately noticable. I got the spark arrestor and installed it right away, do not plan on riding without it, I go in leafy wooded areas from time to time. The sound? I liked the whisper quiet of the stock exhaust, not crazy about the louder exhaust, Its not terribly loud, at low speed putting it is very quiet, its when you run high revs its pretty loud, but we have Harleys and crotch rockets around here that are way louder, compared to them I am very quiet.
My consumer report: Does the Yoshimura improve performance or just make more noise? Both. I highly recommend it.