One slightly disappointing aspect of the GX7 is that since the GH2, Panasonic seem to have abandoned the oversize sensor which allowed changes in format without cropping. Thought it was a gimmick at first but have actually found it to be quite useful in the field as a compositional tool.
I must try to do the arithmetic to see how many pixels are lost with GX7 16MP sensor versus GH2 18MP sensor.
The only actual review of the GX7 I have seen by ephotozine thought the OMD had more noise but slightly more detail but as they were comparing JPEGs I wouldn't place much faith in that especially also as Panasonic JPEGs aren't especially good in my experience.
