I went from an 04 636 to an 06 10R. Truly depends on how you ride and what you expect from the bike. I never thought my 636 was slow... until I rode my 10R and I got that impression in break-in before I ever truly cracked the throttle. As mentioned above, the 10R is less forgiving. I could spin up the rear on my 636, but it took a little effort. The 10R, does it without breathing hard. Plus, the 10R provides breathtakingly deceptive acceleration. The 10R is a better intown ride due to usable power in the lower gears in my opinion, but in the end, it is up to you.