Hi Dave.
I love it! I can't comment on the D800 & how much sharper the E actually is, but I have no complaints at all. I just reckoned, as I could afford the extra at the time and most of us crave that little extra sharpness with lenses( & each of those aren't cheap ) so why not try to improve a tad more with the body on which they're used too?
tbh, I have the 80-400mm lens on it all the time & use my D700 with the 16-35mm for landscapes. In reality I should probably use the 16-35 on the D800E, but the D700 isn't as good for cropping in for bird shots. (I detest changing lenses, especially outdoors!)
Ideally IF they bring out a D400 i'd probably get that for birds/wildlife, sell the D700, then use the D800E for landscape/architecture.
I have found that I need to up the shutter speed though to keep pics sharp/motion blur at bay, but that may just be my old shaky hands.
Forgot to say, I've never done any studio stuff, but it's reckoned to be excellent.