I recently received an Olympus OMD-EM10 for a few days. It is very similar to my OMD-EM5. So similar that they are hard to tell apart (except for being able to see the name on them). Performance and image quality also appears to be very similar. The biggest advantage of the EM5 is that it is weather sealed and has 5 axis image stabilization. The EM10 only has 3 axis image stabilization, but it does have wifi so you can view and capture the images on your cell phone and use your phone as a remote release. The EM10 is also about $200 cheaper than the EM5.

 Happy Shooting!