If you're considering the Oly EM5 then I think you should also have a good look at the Fuji X-mount bodies. Much closer to the 6D in terms of IQ, the handling & ergonomics are great, and the lenses, oh man the lenses... Fancy a 35mm f/1.4 better than Canon's 35L for $600?
The only things that should hold you back from switching to mirrorless are:
- if you need fast AF for sports, birds, etc.
- your existing investment in Canon gear i.e. do you want to keep your 70-200L?
Big feature of the OM-D is the AF, super fast and accurate, while the Fuji cameras are awesome for IQ and yes, those lenses~ The AF department still needs catching up, even going up against the 6D, which doesn't have the world's best AF but I'd say a lot more responsive and accurate than Fuji bodies. While I have a Panasonic GH3, got that for video work as well as a second body to my 5DII. I am impressed with the noise performance, the 5D still feels like it cleans up better but at high ISOs from 3200 and beyond the GH3, to me, retains more detail, and at least doesn't get ruined with banding.
And the AF on the GH3 smokes the 5DII, in daylight they're pretty close, but once lights go dim the Gh3 still gets the focus right on and speedy. And I assume the OM-D is similar or maybe better.
I would agree though the 70-200L is a keeper, if I go two camera set up then I have a WA on my GH3 and a 70-200 on my 5DII, I will see how things go next wedding, but Ryan Brenizer loves the OM-D and has photos to show during wedding shoots.