F*ck me. Are you going all out and trying to break the 3DMark world record or what? I do think that an Antec 900 would be a bit small for that actually as it's only mid tower case. It would be very tight and cramped in there. I recommend a full tower case like the Cooler master Stacker.
Lol..Imma have to work my butt off this summer to pull out a rig like that. It would be pretty cool. but it's overkill. I think one of them will be fine. I do want the 780i as I heard EVGA covers all overclocking problems you might get. I really like the antec 900 tho...looks so cool. But there are a lot of cases around. I can't wait till I get to start picking my parts for real.