GH3 = attempt at Photographic Dynamic Range

Yeah, who knows the nature of their ISO=125 setting ? Not I. Am pretty sure that Bill Claff uses a SNR of 26 dB as a reference in PDR measurements. For a EM5 (rated ISO=200) Sat ISO=107 here:

http://www.dxomark.com/index.php/Cameras/Camera-Sensor-Database/Olympus/OM-D-E-M5

... Bill Claff's site shows the result of testing Anders' EM5 unit as PDR=9.27 EV here:

http://home.comcast.net/~NikonD70/Charts/PDR.htm#OM-D%20E-M5,Ideal_4/3

If we assume that GH3 (rated ISO=125) Sat ISO is around 125, that value is not far off from the EM5 Sat ISO=107, and your results suggests that the GH3 PDR falls short of the EM5 PDR by 0.35 EV.

That would translate to a numerically larger margin (in difference in EV of DR) if the measurement used a SNR of 0 dB (as in DxOmark testing). Nothing that you probably do not already know ...