What are you guys running for fork height (the height of the fork relative to the triple clamps)? My 610 came (used) with the tops of the forks near flush with the upper triple. I dropped them to the second line last year, trying to make the steering a little quicker and lighter. It worked, but the bike definitely still has quite a bit more rake/trail than my WR, it's really obvious when the bikes are side-by-side on the trailer. I just adjusted it down to the third line on the forks. I won't be able to ride the bike for a few weeks at least, but I am hoping this helps. The bike has boat-loads of high speed stability, so I'm not super worried about it getting unstable. That being said, it might be a little bit twitchy with the supermotos on it now... it wasn't an issue before, so it should still be ok, I would think. I use my bike for trail riding, dual sports, and the occasional race, so having quicker steering and a little less stability is fine. My WR has WAY less rake & trail than my 610, and it's still pretty stable (seems like a Husky geometry thing, which I am a big fan of).
I've had my 630 at three lines down since I bought it, stock in the back. No problems w/ stability. .
I have mine down to the second mark and like you have no stability problems to 100+MPH and want as much steering quickness as I can get. What I do notice is more heaviness up front that makes deep silt/sand more interesting. I'm going to recheck the front sag and maybe try more preload or heavier springs and raise the bars slightly.
