In your case, I'd go for the D800. If you had a D700 or even a D7000 it might be a different story, but you are going to gain at least 3 to 4 stops of "low light, high ISO" capabilities. I've never owned a D200, but I assume that the maximum useful ISO is right around 400.
Also, all your lenses are FX, so the change won't be that expensive.
Assuming that the 85mm focal length that you were going to get with the new lens is a priority, the FX format is going to give your 105 a similar field of view. You already own enough lenses at the long end, so that combined with the additional MPs leaves the "reach" issue out of the picture. And, you would gain a huge advantage at the wide end of the spectrum.