As far as I can tell on my mediocre laptop screen, the E-M5's JPEGs deliver a reasonable dynamic range. I don't yet know how much recoverable detail it retains in the highlights, though, as there seems to be a little more clipping in the highlights in some photos than I'd like.
Note that this image is square because I accidentally managed to switch the aspect ratio settings. That's Shawn Barnett from Imaging Resource knee deep in the snow.
(1/1600 sec, f8, ISO 200, center-weighted metering, AWB, 12mm lens)