I can't help you with that question, but do you also use CreativeCow to look and ask for questions, as CC is more versed in DCC application?
Have you also looked at the VideoCoPilot tutorials, as I faintly remember being there a tutorial dealing with morphing a face. I might be wrong though and it could have been Aetuts+.
Since both cameras use 4:2:0 chroma sampling, they are both almost the same, as in not really ideal to do that. But if I had to choose, I would use the 550D/TI2, because of the bigger sensor (almost three times as big).
Here is a very good guide about video compression, and touching the green screen subject: