I am currently installing Konred 540's on my 04 Spectre Cat. We are using the Huber transmissions. Power is up around 1000 HP. 1.21 ratio w/nose cones. The Konred is .800 lower than the XR, so we had to raise the height of the drives to maintain the existing drive height. The workmanship on the Konred is flawless, and the gears, shafts, case, everything make the XR's look like a poor excuse for Mercury. I will be using the Herring 5 & 6 Blade Props, so there will be a lot of strain on these drives. Will keep you informed.
Talk to Bill @ Ohio Performance he is now a dealer.