I suppose the two GTX570s are to be air cooled.
Two important factors dictate the choice of a case:-
1. Motherboard: how many empty slot(s) will there be between the 2 cards?
2. Type of GTX570: do the cards use traditional cooling (ie front-centrifugal-intake-fan-and-rear exhaust)? If the cards use other types of cooling, does it exhaust heat via its front-and-rear or front-and-rear-and-along the entire top length of the card?
These 2 factors will decide how the supply of fresh air and the extraction of hot air be done properly inside a case.
Accordingly, the case should have good fan openings on top (likely for extraction of hot air), on side panel (likely for supply of fresh air) and on front (likely to be fresh air supply).
I cite the HAF932 (not the version with the side window but the versions with mesh side panel fan openings) as a prime example for consideration.