Im trying to find a suitable 5 speed replacement for my t45 since it lasted all of 2 pulls on the new kb set up. Im mainly looking at tko 5 and 600s but also promotion t45s. Its my understanding that the diff between the 500 and 600 is the 26 spline input? Is that the only difference? How well will the 600 hold up to a kb 2.2 on a small hit of spray? How do they shift at high rpm?