hey man, i got a yoshi exhaust also but i cut mine down about 7inches and i have not noticed any powerloss at all. my buddies bike the one i just posted (blue/white with blk frame)has the same yoshi exhaust and we took about 8.5-9inches of his(basicly straight down the middle) but he hasnt noticed any power loss eaither,so you should be good to go if you cut it down. but i do know that if you cut it down more then direct center then you will loose backpressure and def see some power loss. i just chose to take 7inches off mine so i could keep some back pressure and still keep all the power + a nice sound difference. (deeper and a lil bit louder tone). but did you have youre bike tuned for the m4?:cheers