A number of people have commented about my Big Cropper comment and professed that they think they're not one. In particular, the African safari photographers tend to make a comment like this one: "the DX crop of the D800 allows me to still produce 15mp images and get the longer reach benefit. I don't need to bring as long a lens to Africa."
There are several problems with that thought, but let's deal with the last: on safari, you never quite know what you'll need. You need extreme flexibility because a close-in elephant may have you wanting wider than 70mm (FX) and a distant chase you can't quite get to may have you needing more than 600mm (even DX) to do it justice. The typical answer is that you have two, sometimes three cameras handy at all times, all with different lens options. For example, the 200-400mm on one body, a 70-200mm on another, maybe a mirrorless with a 24-100mm equivalent for close to the vehicle stuff. You "crop" by picking up the right camera.
The argument is that a D800 changes that in some way. Not as much as you'd think. First, you need two of them ;~). You still need a "reach" camera and a "less reach" camera. You're not likely to be using DX crop on the body with the 70-200mm (that gives you 350mm equivalent, which overlaps your 200-400mm ;~) You might with the body with the 200-400mm. The question is how often would you be using DX crop on that 200-400mm body. If it's "a lot," then maybe it should just be a DX body in the first place. Either that or you need to be using a TC or just bring a longer lens in the first place.
To understand that, you have look at the pluses and minuses of the D7000 native and the cropped D800: (1) As a DX camera the D800 gains perhaps a third to a half stop of dynamic range over the D7000, and it has a slightly better focus system; (2) The D7000 has a faster native frame rate (6 fps versus 4 fps), has a few more pixels (16mp versus 15.4), and costs a lot less (thus you're putting less value at risk on your trip). There's not a clear winner between the two if you're using DX most of the time to get reach. So many people would be better off putting their money into the lens in this situation, that I'd tend to lead them towards the D7000 just on that point alone.
I'd be remiss if I also didn't point out that a lot of people get hung up on "head portraits" of animals. The reason they want reach is to produce an image that they could get in a zoo. "See how close I got?!" If you look at the work of the best wildlife photographers (Chas Glatzer, Andy Biggs, etc.), you'll find that a lot of the time it isn't animal isolation that makes their best images, it's animal-in-environment. They simply don't value reach over everything else, though they certainly carry reach with them (again, you can't always control your position relative to the animal or what's happening). Yes, you sometimes see extreme closeups from the name photographers, but note what those images are: extreme animal behavior, not just portraits of a lion resting during the day. But those images come rarely. What are you going to be doing the rest of the safari?
My use of the words "Big Cropper" need a bit more explanation, I guess. There's nothing wrong with crop flexibility. We've all been in situations where we couldn't quite get the image we wanted, or perhaps the image we saw wasn't a 3:2 aspect ratio in the first place. Cropping for a valid reason because a situation warranted it isn't bad. Thus, the word "cropper" isn't the key word here. It's the "Big" that's the important word. If you're always cropping, and if when you crop you're always cropping in large amounts, then FX probably isn't the format camera you need. A D800 becomes a lazy (and expensive and maybe even post processing intensive) way to achieve the images you output.
I grew up with mentors telling me "lenses first." I think that's as important today as it was 40 years ago, maybe more so. Let's put that to a little test. Let's say you're going to Africa for safari and you have US$4000 to invest in equipment. Would you (a) buy a D800 and a 28-300mm lens; (b) buy a D7000, a 70-200mm f/2.8 and a TC-20EIII; or (c) buy an OM-D and the Panasonic 100-300mm and have some money left over for other things, like a backup body?
The first option gets you a focal length breathing 300mm (i.e. not 300mm close in), the second and third nets you 600mm equivalent. Even with DX crop we're only at 450mm for the D800 option.
I'll stand by my (implied) comment: if you're always cropping, and especially if you're always cropping in large amounts, buying a 36mp FX camera probably isn't the right solution to your problem(s). Too many people are seeing the D800 as a Swiss Army Knife, capable of doing any and everything. But as with most Swiss Army Knife owners, they'd be better served by the right tool in the first place.
Some people think that when I write something like this, I'm looking down my nose at them and asserting some sort of superiority. Not at all true. I'm trying to help people solve the right problems with the right solutions. I've watched so many people pour massive amounts of money into "solving" some photographic problem only to find that they aren't treating the disease, they're just moderating the symptoms. They'll spend more money down the line until they get to the core of the problem and eradicate it.