I put 27" mud bugs on my 660, I went from 105km to 95 km per hour and the bike was very lazy. I talked to my local dealer about a cluth kit , an employee had the same problem with his 700 grizz, 28" tires. That same day he was talking to a clutch supplier about his problem and they recommended leaving 4 stock rollers in and putting 4 rollers from a 450 kodiak, staggered so everything is balanced in the clutch.( I am not sure if the kodiak rollers are lighter or heavier but what a difference.) Both he and I tried it and it works great, it brought the rpm's back up and both bikes are peppy again. Both bikes lost about 5 km per hour but it is worth it. My bike will go 90 km per hour but it's peppy all the way. It cost me $10 per roller plus a tub of grease.
keith
keith