Consequently, i can't think of one occasion where GPS would have been of any use to me at all.
I admit I find the built-in gps unexpectedly useful because it doesn't add bulk, uses little battery, is always there and you don't need to have a dedicated tracker and add the gps data in postprocessing. Sorting in LR with but map is very nice if all your shots are tagged.
However, I admit I don't quite understand Canon here: 6d with wifi+gps, 70d only with wifi, 7d only with gps?! Sounds like a typical Canon "crippling" product policy to gear up for the 5d4 which will of course feature both. On the other hand it really *could* because of the metal body, you never know with Canon...
You think an EyeFi card is going to perform better than the 6Ds internal WiFi?
EyeFi is a hack in comparison to the built-in wifi, even though Canon's implementation is mediocre at best: You need to set up a virtual access point to connect to the camera from a laptop. But you can remote-control the camera which might be very nice for wildlife shots (read: 7d2).