I have and use both the D700 and D800E. I consider them equal, except when planning for a large print when I naturally favor the D800E. For smaller prints, I find Russ's coments about downsampling right on. At high ISO, I believe noise no more of a problem with one than the other.
I find any difference between the D700 and D800E when making small (8x10) prints is negigible -- the D700 prints need a slightly different sharpening process but, in my opinion, the images turn out essentially equivalent to the D800E. Ditto for images prepared for internet use. There are slight differences in the way colors are rendered.
For large prints, the D800E is king regardless of the lighting situation. I am still amazed at times with the images that come out of that body. But, the D700 is still an excellent excellent body and I continue to use and value it. For the past several months I have kept a 24-120 f/4 lens on it and I use either the 24-70 f/2.8 or the 70-200 f/2.8 on the D800E.
From your post, I would expect the D800 will not be signifcantly better and I would suggest borrowing or renting a D800 should precede a decision to purchase one. Be careful. I expect if you try it, you will love it.