Coming in late on this thread so excuse if I say something that's been said already.
I have a 5D-I and an M8, only used a Mk-II for an afternoon, likewise an M9, so I can't weigh in on those models other than to say that the MK-II didn't wow me more than my Mk-I, and neither did the M9 wow me more than the M8.
As for color, I don't understand where people are getting their comparisons from. Even if you limit it to RAW/DNG and rule out JPEG entirely, the color still depends within each camera on the raw converter and the chosen profile. I use Capture-One v.4 with my M8, and there are 3 OEM profiles, none of which I care for. The one I use most of the time was made by David Farkas of Dale Labs, and occasionally I use one made by Jamie Roberts. They are all very different in the way they render the colors. Plus, I always use their "film profile" called "wide latitude" (or something like that). Before v.4 I used CS2's ACR which I found much better color-wise (and other ways too) to Capture One LE that came with the M8. OTOH I've tried Capture One for my 5D and found their profiles much less pleasing to me than either Canon's proprietary converter or CS2's ACR. Bottom-line, depending on what converter/profile I use, I could form totally opposite opinions comparing cameras.
I also do not see a whit of superiority of prints from the M8 than the 5D. If I processed the M8 prints using my 5D workflow I'd say the M8's prints were worse; vice-versa if I used the M8 workflow on 5D files. If I standardized on a single workflow for both cameras, I might say they both were worse than a DLux-3 if that workflow happened to be optimal for the DLux. I'm not into comparing anything but final prints, because that's the name of the game for me. In that respect, the IQ of both cameras is equal in my estimation, except the 5D is at least 2 stops cleaner in the noise department from 800 up. However when the 5D does get noisy (ISO 3200) the noise doesn't look as film-grain-like as the M8 at 2500.
Focusing, I've never had a problem with the 5D's AF in low light with fast lenses (35/2, 50/1.8, 85/1.8), or with manual-focusing those lenses (or some fast Pentax and Nikkor manual lenses adapted to the 5D mount), and that's with the standard focusing screen. And I'm nearsighted w/asitgmatism, need bifocals, and am close to the half-century mark.