2018 UPDATE: I have now switched entirely to a mirrorless Olympus system for my professional work and am thrilled with the results. Here are my findings in the three years since the original comparison article was published.
Yesterday, I posted this side by side comparison to Facebook as a simple test. One image was captured with a full frame DSLR and a professional quality lens totaling approximately $2400. The other was shot with a small mirrorless camera with a micro 4/3 sensor and a prime lens totaling $899. Both were captured in RAW on a tripod with the exact same camera settings and auto white balance. They were imported into Lightroom and were not sharpened or adjusted in any way, only saved for the web.
As you can see, the results were quite similar, making it quite challenging to determine which is which. This was further proven by the variety of guesses from the Twitter and FB communities. Some were able to see the difference, while others couldn't. Now, I'll reveal the camera types.
Do the results surprise you?
Here's a larger view of each image.
My take on it
Considering that an entry level Olympus with a micro 4/3 sensor can actually compete with a full frame DSLR on image quality, I believe a major shift is coming to the industry sooner rather than later. Yes there will definitely be pixel-peepers who dispute that. This is not for them, but rather to help YOU find the best tool for your specific needs. Do you want to spend an extra $1500 and carry more weight or would you be better off with this alternative?
The images out of the mirrorless have more than enough resolution for publication, web, and print enlargements. Granted, the 6D definitely offers better detail at larger print sizes. Still, at a fraction of the weight and price, one has to really determine what their priorities are. For travel, scenic, everyday work, the OMD EM-10 has repeatedly proven its worth. In addition to the excellent files one can capture with it, the functionality is actually superior in my opinion with more focus points, EVF, to name a few. Having said that, I still reach for the DSLR for sports, wildlife, and aviation. I feel the AI Servo and instantaneous response are more conducive for high-speed situations. Yet with advances in mirrorless technology and a wider selection of available lenses, I do wonder how much longer that will be the case.