for features you really want 2x 6pin PCI-e connectors + 2x 6+2pin PCI-e connectors, that would allow you to run 2x6pin cards in crossfire, or the 6+8pin cards if you needed. I don't really think you could go far wrong with any decent Corsair, Seasonic or Enermax, although my Pref is on the new (unreleased) X series from Seasonic, which is a redesign of last years X series, or the AX from Corsair.
Affordable is a matter of opinion though, none of them will be cheap if you are looking for something that is reliable for crossfire at around that wattage.
The Corsair HX750w is very nice, but it is also quite expensive.
I am sorry for not really answering your question, but in the past I have had a crappy generic PSU go bad on me, causing random restarts due to loose ATX connector pins, that didn't present itself for a good 2 weeks after installation, and a Thermaltake 480w unit that decided to die one day. I also had a 520w OCZ Powerstream back in the day that cooked itself. And before you all jump to say there was some power problem, they all ran through a hefty surge protector, and the Powerstream was even through a UPS after the surge protector. I guess I was just lucky ;)
I know that generally what you put into the PSU will be rewarded, if by nothing else, just a lack of failures/ problems.
Hope that helped a bit.
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