Okay, so I know there's been a lot of topics like this recently but I believe that advice might differ from one person to another. So here goes...
First of all, I would like to emphasize that photography is strictly a hobby
(although it does come in handy with my image processing research from time to time). My previous system was a 60D with the following lenses: EF-S 15-85, EF 50/1.4, Tamron 70-300 VC USD. The body and the 15-85 lens have already been sold to facilitate the move to FF.
For my type of photography, I enjoy doing landscapes, macro (although I use an extension tube for budget reasons), portraits (still subjects mostly... and my pet dogs!), and general travel photography.
So here's the thing. I understand that the 5D3 is by far superior in terms of AF functionality. With my 60D, I've had no problems dealing with focus though. Sure, I have a hard time tracking my running dogs and focusing spot on when there's fast motion but is that really just the difference? To give you an idea of what I've shot, here's some samples:http://500px.com/nightsky87
Is there anything wrong with the focus on those?
On the other hand, the 6D has the WiFi functionality and low light focusing capability as well as UHS-I support for much less. So, so far I'm leaning towards that. It seems to have a similar AF as the 60D and even the controls! Before anyone says anything, I find the remote control/monitoring capability of the 60D (with a USB cable and my Nexus 7 tablet) great especially for my research work.
Finally, there's the good ol' 5D2. Is there really any reason to go for it instead of the 6D? Again I'll say this before anyone complains, I know there have been little reviews on the 6D but most seem to say that the AF system works fast so that might be good for me. So lets just work with what we know at least?
So basically, any other insights might help. Anyone?