I recently also did the same upgrade from 550d to 600d. For me the main things were articulated screen and digital zoom. But it came with a price - 600d has worse audio hardware and really you can't use it without a preamp in normal environment where you have to apply some analog gain in camera. The hiss is really loud if you set the analog gain more than +15. Good that I had a Zoom h1, which I could use as a preamp, that way the sound is ok. I have the Rode video mic, which has no +20db option like the VideoMic PRO, I guess with the pro video mic the sound would be better,