I'm not a wedding photographer, but I do shoot a lot at high ISO (sports) and I do events, too.
I can't imagine how the D800 will fail you. Do you really shoot at > ISO 3200 all the time? If you can use your D7000, we know it's good to about ISO 3200 or so, and the D800 is surely not going to be a lot worse at high ISO as they have very similar pixel sizes and density. (OK the D800 is slightly denser, but it's also got the benefit of a year and a half more development.)
I assume without inspecting your profile that you must have some fast glass. Let's assume you have typical f/2.8 glass, and that you require 1/125th shutter speed minimum to assure crisp results. At ISO 3200, 1/125th, f/2.8 is EV5, described as "Night home interiors, average light. School or church auditoriums. Subjects lit by campfires or bonfires" Seems reasonable to me. Two stops less light - ie f/1.4 glass and ISO 3200 - we're a full stop below "Candle lit close-ups." And remember that we're assuming ISO 3200 and 1/125th. The latter is quite pessimistic for focal lengths < 70mm and the former is pessimistic given that Nikon rate the D800 at 6400 "in range." That won't be noiseless, but that's what the D700 does now. You've got at least two stops additional to work with, assuming that you're unwilling to do post processing to minimize noise. Remember that even if the D800 has more noise than the D700 on a pixel-for-pixel basis, it's also got 3x as many pixels. If you downsize to 12mp, the per-output-pixel noise is going to be less than what you are used to seeing from a D700, not more. I know, 12mp is perceived to be not very much any more, but 12mp is a native (roughly) 14x9 print. What proportion of your wedding prints are significantly bigger than that? I'd guess about one per job, and for that one you can devote some post processing effort to the single image. If it's significantly bigger than that, you're struggling with upsizing the noise today anyway.
I don't get why everyone is so freaked out about the D800's low noise ability, even on a per-spec basis.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!