Seems 5.5 is not applying MaxQuality sharpening.
Is this a direct export from Premiere or did you send it to AME?
I have found a sligt difference when doing this.
I'm not sure if I sent the video that I capture the picture from to AME or not; however this morning I tested if there was any difference in my cs5.5 rendered video if it was sent to AME vs premiere pro. I didn't notice any difference between the two.
Ok, I've resolved my issue.
The solution was that I needed the mercury playback engine (MPE) enabled. My card isn't "adobe supported" for MPE; however, it is good enough to use it(gtx 480).
Using this guide I was able to enable MPE with my card: http://www.studio1productions.com/Articles/PremiereCS5.htm
My previous renders (cs 5.0 & cs 5.5) were done with MPE disabled, but I guess I needed MPE enabled in cs 5.5 to get the same results as cs 5.0 (MPE disabled).