Following Bryan Fong’s advise (Nikon Professional), it depends on the genre you specialize in or the kind of end product you want to achieve. Between D800/D810/D810e and D700/D750’s specs, they have more differences than similarities starting with the megapixel count. Set aside the ergo features (unless you question Nikon’s R&D and QA), it is more about what each can do when your need arises. So what kind of photography do you do? From there you can start matching it with the tech data.