I'm all with you on an overkill system... But, even if the budget is infinite, I'd go for two 680's for now (again, if you can find them) tops, surely you wouldn't notice any gain from four over that for months (or possibly years, lol).
You should look at more radiator space too, especially if you're looking at multiple GPU's. I've got two 240mm rads in my case now, and am still above temps I'd like to be at. At least another 240 would be smart for four cards if your set on that.
edit: 4 won't fit in the 800d either- only 7 slots on back