Mmmm. The usual suspects are Video Card defect - but yours worked under Vista.
Bad RAM modules - but that's nice RAM. Is it on the "Approved & Tested" list?
Poor power - But that is a nice power supply.
Nothing easy pops out. But here are a couple of ideas:
For a clean install with problems it would be best to simplify the setup as much as possible. I would connect only one hard drive (disconnect data and power just to eliminate power issues during W7 setup). And I might install the OS with only one video card and deal with the crossfire thing after getting by the install roadblock.
As a rule I always take the opportunity to flash my BIOS to the latest version before clean installing an OS. There may be improvements made since the new OS came out. I might also help to reset the BIOS defaults before you install. Just configure SATA as AHCI before doing the install, but leave everything else as default.