My product offerings stop at 40x30 inches. Prints look good, providing they are sharp and well crafted. I shoot with either my OMD or more rarely my 5DMkIII (set at Medium RAW which is think is 12MP).
I do my upsizing using Photoshop's Bicubic Smoother which to my eyes does a better job of the third-party resizing packages you can buy. Remember that larger prints are almost always viewed from further away than smaller ones.
You can do a test by resizing your print on the computer to the size you want it and then cropping out say an 8 inch portion and printing that, and then holding it away from yourself to the appropriate viewing distance.
Thanks Lindsay, thats good to know as I've had a few prints recently from my D600 (& Sigma 35mm) which looks incredible at A2 size so I wanted to be sure I would be able to still do prints (if they're sharp enough!) at that size.
I'm seriously considering moving on the D600 and picking up an EM5 (or EM1....)
Chris, it's going to be the quality of your lenses more than anything else which will make the biggest difference to the quality of the final product. Given how wonderful many of the Micro 4/3 lenses are, I don't think you'll have anything to worry about! In fact the Micro 4/3 lenses are quite addictive.
I have very large prints around my home and viewing area which were taken with cameras much older and more primitive than the OMD, and they looked terrific. Like I said, good technique, good glass, and careful resizing. I think you'll be fine.