E-m5 vs. Sony Rx1

My two cents:

I can't see any reason why a full frame sensor is desirable or necessary when paired with a 35mm lens. It doesn't make sense.

Full frame shines when you want to create shots with very shallow depth of field. You won't be doing that with the RX1. You will not be doing that with a 35mm lens. In fact, the traditional use for this focal length is to portray subjects within their surrounding context.

If you need full frame sensor then you need it on portrait lenses and/or telephoto lenses for sports and wildlife, shots where DOF matters.

The other possible reason I can think of is for landscape shots that will be displayed at very large sizes - in this case you will probably want to use a wider focal length.

Its also worth pointing out that the RX1 isn't really much smaller than the EM5 at all, especially not once you add the viewfinder: http://j.mp/12V2xtO