This may have been covered already ... is there an adapter to use R lenses on a Sony A55 mount? Or does the R mount have to be swapped out?
The incomparable R 50/2 is pretty small, would be an interesting lens ... perhaps easy to use with LCD manual focusing?
I've noted that the quality and character of the Leica M optics has translated nicely on the NEX5 ... so the A55 sensor seems up to it to good degree.
I also have an R135/2.8 laying around here that is 1/2 the size of the Zeiss ZA135, and remains to this day one of my favorite longer portrait lenses because of its sharpness, yet gentle and forgiving character.