Over the last couple of years GH2 has become my "pick up and go" camera with 14-140, 100-300 and 20/1.7. (I have DPmerrills and 5d2/Zeiss for other stuff).
I'm happy with that except that in that role I would like the body to perform better at high sensitivity - I feel anything above ISO 800 is unusable although I admit I haven't tried any specialist noise reduction software.
I would consider it worth getting a replacement for the GH2 only if it delivered 2 stops or more better low light performance, especially while I can still get a worthwhile price for the GH2 on ebay. I am realistic about the ceiling on IQ imposed by those lenses (except the 20mm). On the face of it the Panny GX7 looks like what I need (well want would be more accurate!) but those indications of image quality available still suggest the OMD E5 or the EP-5 (latter too expensive with vf) are better. However, a bit more digging, e.g. on Imaging Resource website suggests these comparisons based on jpegs and that Olympus routinely apply more in-camera sharpening than Panasonic.
I wonder if there is an upcoming review of the GX7 on LL which might compare IQ to OMD?
Someone did this test, I just don't remember where. Try google you'll find it.
But it depends on how you look at it. If your using a full frame Canon and set it at F4 at 1600 iso and shoot a gh3 or omd at f. 2.8 at 800 iso you have essentially the same exposure, same depth of field and pretty much the same noise level.
I've test the omd5, the gh3 and the Canon 1dx in the same settings shot the way I mentioned, there is virtually no difference in raw. The 43 systems tend to come out of camera either looking noiser (OMD which is sharper) or smoother (gh3 which is a little less sharp with their 2.8 zooms but has better color) and a 1dx which is smoother but not more real detail.
If you work the files in the latest C-1 or lightroom (I prefer C-1 and Irident Developer) and are careful at moving the color and luminance sliders, and sharpening sliders, the image is almost identical to the 1dx.
Now the 1dx will go to much higher iso than 1600, though once past that it's smooth but loses DR, depth and some sharpness and the detail can be recovered some at let's say 3,000 iso, but the file will suffer.
The OMD in comparision to all the cameras I've mentioned is much, much sharper, some of it do to processing, some the olympus primes which are very fast, very sharp.
The OMD though is a much more difficult camera to work than the pansonic which is much more intuitive.
Really in 43 the best of both worlds is a pana with the oly primes. You get sharpness, better color and a more usable camera, probably the same would hold true for the gh7, but even the gh7 pretty much tops out at 1,000 iso.
The real king of high iso and quality is the fuji with the x trans sensor.