Hey guys, I currently have the choice between a 4.25" rear with cush drive or a 5" rear without cush drive. I'd prefer the 5" so I can run a 160 but the bike is going to be ridden on the street just as much as on the track. Is the cush drive necessary on this bike? I've yet to hear about modern WR's having transmission issues but would like some more info on it. Thanks!