Is the EM5’s Miss-Stated ISO concerning to you?

Why not just take a look at the DxOMark RAW-level test results, then ? For SNR at 18% of maximum of linear sensor illumination (full SNR data is also available when accessing the individual camera information web-pages), and when viewing the graphs in "Screen" mode (because the pixel-resolution is the same in all cases), the following information regarding the EM5, GH3, and GH2 can be found [in the Measurements, SNR (18%) graph, "Screen" mode] here.

The DxOMark information available indicates that at the manufacturer rated ISO settings:

The SNR (18%) of the EM5 at ISO=6400 is 1.6 dB (0.266 EV) higher than the GH2 at ISO=3200

The SNR (18%) of the EM5 at ISO=6400 is 1.1 dB (0.183 EV) lower than the GH3 at ISO=3200

The SNR (18%) of the GH3 at ISO=1600 is 0.4 dB (0.066 EV) lower than the GH2 at ISO=3200