3:2 and 4:3 equivalent how?

Perhaps so. Those are the numbers reported in the ORF RAW image-file meta-data. I believe that I did the calculations correctly.

It is also notable that the E-M5 image-file meta-data is reporting "Image Width" and "Image Height" in it's tag-values only.

GH2 RW2 4:3 AR RAW image-file meta-data reports "Sensor Width" = 4760 and "Sensor Height" = 3472 (considerably wider in pixel-width, representing an extra 3.3%), which DxO Optics Pro is able to access (more similar to what you display with your Capture One).

There may exist some normally masked-off photosites within such extra (horizontal) dimensions intended for the purpose of reporting black-level offsets which are not necessarily usable photo-sites.