I just put new MDI's on my 550. They are a damn sight better than my old, original shocks. They feel pretty stiff, as it says on the loudfastugly website, but then I only weight 155, so maybe 200 lbs. will feel different.
I wanted something better, like Progressives, but I've been pouring money into this bike and just wanted something that was safer than the crappy old ones (which were on the top notch and still bouncing like a cheerleader).