I have now tested Live View with my two other Sigma lenses 24-70 and 70-200.. live view behaves a little better with the 24-70, so it appears that it may be a lens issue.
I am most surprised that the 50mm prime f1/4 is the worst offender, because its only a couple of months old and is quite sharp for taking shots via the viewfinder.
I read a post i found on another site via Google that said that 3rd party lenses may have an issue with the D800 due to Nikon updating the communication protocols. (i have no idea if this is true or not)
Nikon Rumours, also posted an article last week that suggests the D800/D600 will also soon get another firmware update, they mentioned some live view fixes.
A check of the Sigma site does not show any details about firmware updates for lenses .. pleased to hear from anyone who has been successful in getting their lenses updated.
Either way ... its looks (even at its best) like Live view is really only usable for static shots using a tripod, handheld or fast motion are not likely to result in good photographs.