An ex-racer friend of mine in Springfield suggest going with an M4. I've ridden a couple of gixxers and a Katana with the change to an M4 and there's a very noticable power increase. They are quite deep and throaty, but not too awful loud at an idle. Another option is a Two Brothers X Metal can. They seem to hold up very well and sound great too. Haven't ridden anything with the Two Bros. though, so I'm not sure about the power increase. You shouldn't need a power commander or any product like that with just a can. If you go full exhaust you will definately need to remap your system. Getting rid of the spark retarder will help considerably if you add just a can. You will get a better low end response once the retarder is taken care of.