Did you actually try the D800, and are you sure your issues are hand shake vs. a D800 focus issue?
I think the whole "you can't hand hold a D800 due to the 36mpx" is nonsense. Your profile shows you have (had?) a D300. The D800 pixel density is not significantly different than a D300 (crop sensor), which means that for a given amount of camera movement approximately the same number of pixels are going to be blurred as on your current camera. And if you are using the whole FX, it means actually more apparent sharpness for a given lens/motion combination.
But having gotten my D800 on day 3, I did find a need for rather extreme AF fine tune. Is this a defect or design? Who knows, but if I left everything at zero, more back and front focus led to more soft shots, especially on wider lenses. I am still not happy and planning to send it in for adjustment.
I also found that the tracking/continuous focus was more erratic than my D300, grabing surrounding items too aggressively, yielding soft images.
Sorry to ramble, but my suggestion is to make really sure it is hand shake that is your issue before you change cameras to fix it, especially to the D4 which has a similar AF system (I do not have a D4). If you were happy with a D300 and your hands, my guess is your problem may be elsewhere.