Thinking of switching from M43 to NEX

You are right, in theory an APS-C sensor should have 2/3 of a stop more of dynamic range at base ISO.

In practice, at the moment the advantage of NEX over the OM-D should be a stop more, because OM-D raws do not capture all the dynamic range of the sensor at base ISO (I think because it's over the 12 bit of the raw).

Still, the OM-D has a dynamic range comparable with the best present Canon FF (that does not use Sony sensors).

And Canon FF has a large gap against Nikon FF, at least 6-7 times the theoretical gap between 4/3 and APS-C... people should trow their Canon equipment out of the window and go Nikon, shouldn't they?

I think people like to talk about dynamic range, but they don't really care, maybe because the dynamic range of modern cameras is 5-6 stop over that of the monitors, and it's all about JPEG processing or RAW headroom, where "dynamic range" becomes "a bit of noise in the shadow when I bring up the shadows of 4 stops"

In the future, maybe fast electronic shutters can give us unlimited dynamic range for every sensor size. (something more "unlimited low ISO")