Just bought 5D mark III - heard Nikon D800E is much better image Quality? did i make a mistake?

John Motts wrote:

If I were still shooting ballet with a 5D mk2 I would definitely want to change because of its poor, out-of-date focussing system.

With the mk3 though all the mk2's weaknesses have been addressed so I wouldn't want to change at all. I'd definitely stay put.