Michael is absolutely right. When in the hands of a good photographer, the differences between medium format and D800 images are almost nil. A long time medium format pro friend of mine is currently weighing up his options, as he has also seen a significant change in IQ comparison tests. He can re-equip himself with all the Nikon bodies and glass he needs, for about 1/3 the cost of replacing just the essentials of his current medium format gear. The only thing making his stop and think is that it all seems too easy.
Leaving aside actual resolution, several high end Nikon and Canon bodies are knocking on the medium format door, in terms of IQ.
Previously, medium format was so far ahead that it was impossible to even think about having this conversation.