Just wanted to make a willing post plug to the folks at Traxxion Dynamics. They rebuilt my EX650 rear shock, and did, by all accounts, an awesome job. While it will be months before I can test it out, one of their techs actually raced an EX before, and I think did some work with a Moto-ST team that raced in the states. They sent back the shock with a shock dyno chart (I have no idea what it means), and of course it is spotless. Spring rate was correct for my weight, and some revalving magic was done, as well as a recommended ride height setting.
Their website is: http://www.traxxion.com/
Give 'em a call. Friendly folks for sure. I plan to send my supermono forks to them as well. I need stiffer springs to suit my weight, and Mike and the gang think they can help. Worth it from my perspective. Sort the handling first, then spend money on the engine.