I think Mikael Risedal has a point, in absolute terms, but he's taking it (or trying to) to a level of scientific precision that is of scarce relevance on the field. It's like arguing if you should put 100g or 101g of sugar in your cake.
Sony sensors perform better, we all know it. If someone had to upgrade to FF right now I would advise him to buy a D600 over a 6D, that's sure. The 5D3 is quite another camera though, with a set of features that are fundamental for the professional. That said, an amateur would find much more value on the D600, while the professional can't rely on it when it's time to nail the shot that makes you bring home the dinner.
My 2 cents.