Fujifilm X-Pro 1 or Panasonic Lumix DMC-GH3 or Other?

If you go the M43 route either Olympus OMD EM5 or Panasonic GH3 (and given you have implied that smaller is better and shown no inclination to shoot video, the OMD EM5 would appear best suited), you are probably better off with the Olympus 60 2.8 macro instead of the Panasonic 45 2.8 macro in addition to the Panasonic 12-35 2.8. It is much cheaper - US$500 v US$720 - and just as good i.e. excellent.