depending on how wide the trails around you are should decide how wide you want to make it. also if you really want some good power you gotta dish out a good amount of coin. seeing as you basically have a stock motor there is a bunch of cheaper priced mods you can do. however i would make it a 10 mil if i was gonna do up a bike. it will have so much more torque and power depending on what setup you go with. call cam at redline racing. he will point you in the right direction. im not sure if your ready for a 10mil though if you think your bike is really fast already... some good advise i can give you is spend the extra money that you really dont want to at first and get it done right the first time around. you'll be happy that you did and will save $ in the long run