the AF system may seem new but using the center AF point there is absolutely no difference. And the -3ev doing wonders at low light is yet to be seen. I am usually pro new tech adoption but if a 5dmkii can be had for cheap (and it can be now) - there is no point not choosing it.
shutter spped of 1/4000 and 1/180 flash sync is cripplign kind of. Wifi and Gps are nice to have but not a great add on for most folks. I seldom use the gps on my Panasonic P&S - eats battery.
i rather pick up something that does somethings very well rather than a jack of all trades. The 6D is nice and I would see a huge market for it as a secondary body for many pros.