So, I have a 6D and a D600 in hand right now...

I'm enjoying an E-PM2 with touch screen shutter release and know what you mean about fast and accurate focus anywhere.  But I also have a 5DMKII and know what focus and recompose is all about.  I'd agree however...5DMKII, D600, 6D...they are *all* focus recomposers by design of their AF point coverage.  And in that regard the 6D with the most sensitive in center-point focus recomposing gives it the largest real-world advantage of the 3 mentioned.  Of the three the 6D is also the smallest and lightest (footprint and size of a 60D), and has the best high ISO...all of these I feel would be of interest to someone also shooting MFT.  Dynamic range and clean shadows is something my E-PM2 already gives me but low-light the 6D can still have some clear advantages.

I'd bet you might even like the 6D more just because the 40mm f2.8 pancake exists in one camp and not the other.