Sun 13-May-12 08:14 PM | edited Sun 13-May-12 08:17 PM by AreBee
For my D3x (I figure it makes no difference in this discussion that it is not a D800) I shoot exclusively RAW and use slot 2 as a backup for slot 1. In the event that both slots become full I would overwrite slot 2. I say would, because the situation has never arisen and likely never will: I shoot very few images by most people's standards.
My reasoning is that I retain a backup copy of photographs for as long as possible before having to overwrite slot 2 with (additional) images.