A friend of mine who lives a long way off--so I can't check it out for myself--said that she shoots her D600 with a DX lens, but doesn't let it automatically shift to DX crop mode. Obviously she will have to crop off the unusable area. I almost always crop everything anyway.
If that is also possible with the D800, would the scene still appear about 1/3 smaller? Yes, I know I would be going against the way the camera was designed. This appears to me to be a reason why I might want to rent a D800 to explore my questions. Right now, it's looking like I am going to have to stick with my D7000 or its replacement/upgrade. Wasn't going to get rid of it anyway. I would just like to travel with as few pieces of equipment as possible.
I'm afraid that the D800 won't be suitable for shooting track & certain other sports, requiring a faster frame rate.