The maximum PSU lenght with 2 x 340mm video card is 6.7". I haven't checked, but you can fit most ATX power supply.Yeah, the SilverStone's will hold up 11in cards like the 5870. The Qv2E will fit it though. Any word on what is the biggest PSU that can fit and still have the long cards?
You can fit any PSU with 2 x 263mm (or less) video card.
You should be able to fit it in the Siverstone SG01/SG02 except for the SG01-SW (all aluminum one). The HDD cage is in the way I believe (to be checked).