GH2 vs GH3 - Long Exposures and Astrophotography (Test shots inside)

Sorry but what are you trying to prove with this comparison? The GH2 was given 2 EV more exposure (f/1.4 rather f/2.8, shutter speed and ISO the same) and thus reaches a brightness where you can see the noise. The GH3 image is pretty much at black level so less visible noise.

While the GH3 probably does better than the GH2 for noise at ISO 4000, this doesn't tell us a whole lot about the visible difference when the two are shot under comparable conditions.