Is there a good example of an similar sized image shot on a D700 and 5D
http://www.imaging-resource.com/IMCOMP/COMPS01.HTM
This site compares images from pretty much any camera available (you have to click 'all cameras' at the top of the screen, otherwise it only compares current models)
It's somewhat limited, it only compares camera jpgs with standard settings, but it's something to go on.
The 5D classic and D700 look very similar up to ISO 1600, after which the 5D obviously can't compete (it doesn't do any higher than 3200, which is only simulated by underexposing at 1600 and increased brightness)
The 5D has more chroma noise in the comparison (but this could be chroma NR from the D700's more advanced jpg engine), but this is very easily removed with noise reduction.
Detail looks the same between the 5D and the D700, I think the focus points are slightly different in this comparison, because the 5D looks sharper on things closer to the camera, whereas the D700 looks sharper on objects further away from the camera.
In the 5DII vs D700, the 5D II has more detail anywhere bellow ISO 1600 (thanks to 21mp vs 12), and the D700 has a touch less noise at the higher ISOs
What FX nikon lenses do you have? For landscapes, the 5D classic is probably just as good as the D700 for file quality but quite a lot cheaper (also lacks newer features like the good screen, sensor cleaning, live view and such (it's about the same as your D200 for age of the technology)), and if you don't have any good wide angle FX lenses for nikon then it'll work out cheaper overall.
If you can get used to canon's control system and can live without the newer technology, the 5D is the cheapest way to get superb full frame quality.