I've thought about the 5DIII, its basically very very close to the 6D. I could get the 5DIII body (greymarket) for an insane good price now, but again....with hope of something just a bit better floating around I keep wanting to wait. I probably will wait, but I still want to rent the 810, just heard to much about it I want to see what the fuss is about.
Ideally I'd like to be able to afford a new body while keeping this old one. Especially by the time a new model comes out an I don't know how much an "ancient" 5D2 will be worth. Currently I guess it could pay for a nice piece of glass if I had another body. Its still very young shutter actuation wise (if you can believe it) so that's a good thing.