I have an HMF Swamp Series XL and HMF optimizer on my 07' Rincon. My buddy also has an 07' Rinny with no mods, and mine definately has more low end, and it also rev's out quicker. The XL exhaust it a little loud, but a quiet core fixes that. I haven't encountered any problems with the optimizer yet. I cannot remember what the top speed was before the mods, but mine tops out at 63mph before the govenor kicks in, and there's still a tad bit more throttle left.