I hate to say it, but the Nikon looks better considering price/performance. It doesn't matter to a professional anyway, as the 5d3 will be a cheap body for someone who can shoot sports.
I am an amateur, and as such love landscapes/street photography. Would like to get into doing model shoots, as well. I may keep my 5dII and eventually upgrade my d7k to the D800/D800e. The 5dii is an excellent dslr even though it's a little long in the tooth. I have never looked at a picture, other than WA taken with a 17-40L, and thought "this is not sharp enough for me!!" The 35L is a stunner coupled with this body.
I don't think the new 5d3 will be a significant upgrade in IQ for broad daylight shots. I just don't really believe it. If I needed 6FPS, 61pt AF, and other improvements I would buy it ASAP. As such, I think I will stick to my gun (5dii). It continues to serve me well. And besides shadow noise (which I can handle), it does what I need it for.
The one spec I will hate to admit that the D800 has is USB 3.0 support. Just built a brand new custom PC and it has a couple of USB 3.0 inputs. Coupled with my Seagate 2 TB 6gb/s HDD, the D800 would be a killer camera. Maybe in time I will have one. Until then, I will support Canon.