It seems that most actors are pretty good at impressions. Probably from pretending to be their favourites when they were little.

Yes, I loved McKellan's change to Fassbender's alpha male pose.

I feel like Fassbender is a little more in awe of McKellan than McAvoy is of Stewart. McAvoy seems very comfortable with Stewart, where as Fassbender has just the slight air of speaking to an elder statesman.