i was thinking about doing a full m4 if i keep mine. the site said it adds about 10 hp

 

yea 10 peak HP but also, when you get it mapped, it smooths out the powerband all the way across, so your bike may be running stronger at all RPMs...except the lower ones, where it will be a bit worse due to reduced backpressure.

also note the weight savings of the aftermarket system...it's very significant...

yea K&N is crappy...but it's great cause you can reuse it, but not a must do mod like most people think.