It's not going to consome 700wts, not even 4 beefy cards, but with you're whole system and the cards running under heavy load they want a good overhead, otherwise companies would get huge complaints about crashes and lockups due to insufficient power.
Are you really concidering quad SLi though? I think it's pretty safe to say anyone's CPU would bottleneck before they needed all that juice but I suppose there must be benifits.