It really all comes down to what you want to shoot. But with the D600 being only $100 more expensive than 5D2, I hate to say it but the D600 is a much better choice overall. Not to mention Nikon has great lenses and cheaper pricing too. Nikon seems the most logical choice.
Provided you can even swap lenses, then yeah..the issue comes down to your investment in gear...
To try to defend Canon here, to make up for all my complaining...Canon has some of the most amazing glass out there, the new 24-70 II is... Shockingly, worth its $2300 price tag from everything im hearing (It beats the 24mm TS-E in resolution, Wide open) the 70-200 f/2.8L IS II is pretty much the best 70-200 out there, The 85mm f/1.2L is legendary, the 135mm f/2L is also just one of "those" lenses, The 35L may be long in the tooth but its similarly one of THOSE lenses, The 50L might be controversial but to me its one of those lenses I'd really love to own someday....
The problem with the D800 is simply lenses to be honest, there ARENT that many lenses that can feed that sensor's need for resolution, even their best lenses are struggling, Canon seems to be taking the approach of "having all those megapixels is useless if your lenses cant resolve enough to take advantage of it" sure it doesnt mean the D800 is -wasted- or anything, Just pointing out that unless your system is filled with Nikon's latest and greatest (And mostly prime) lenses you're probubly not going to love the IQ from the D800 because your lenses cant deal with it...
Not knocking Nikon's glass, A lot of it is absolutely spectacular, the D800 is just one demanding you know what...
Which might actually be justification for the D600s existence, it could be the camera for those who are running FF bodies but have a collection of older lenses that simply wont cut it on the D800's demanding sensor... Sure $900 might not be the biggest price difference.. Unless you suddenly have to replace 2-3 lenses on top of it...
And perhaps this explains why Canon hasnt pumped out a D800-like body with high megapixels, Canon knew that their bread and butter lenses that pros use, with the exception of the 70-200 f/2.8L II IS, were not going to cut the mustard, And so instead, they're updating those lenses and polishing them, So when they drop a 48 megapixel dynamic range monster next year they have the bread and butter zooms that pros use to go with it...



