"unless you are into shooting above ISO 3500" ===> So why do you want mrk II AGAIN???
Have you try mrk III yet? Better AF, faster frame rate, and better ISO(low light)...pls don't tell me these features are NOT worth it.
I sold my 3.5 year old MK II and bought a MK III, and do mostly low light shooting. The MK III was not worth it to me. I use center point, and its about the same accuracy as the MK II. IQ is the same up to ISO 6400, and AF on the MK III is slower at higher ISO's, often 3 seconds to turn on the focus light at ISO 6400.
I also have bought a D800 along with some high end lenses which I am trying out. At high ISO's in low light, its worse than both the MK II and MK III, so its going on the block. It is great in good light, nothing can touch it in the price range, but only if you have the best glass, can you get the extra resolution, and just a tiny bit of error in AF, and you lose the advantage. I've had to take a dozen shots to get one that was perfectly focused when using a "D" lens, the gold ring "G" lenses are better. Nikon lenses seem to have the same or even more variability in AF than Canon, and the D800 lets you see that in spades.
I tend to think that 22mp is a pretty good match for most of the current lenses, however there are some that are better, particularly in the Canon lineup. Unfortunately, Canon is also charging a big premium for those. The Canon 100-400mm L is a good reason to use Canon all by itself, there is nothing to touch it in the price range in the Nikon lineup, or third party either.