I just spoke with XFX, and they said despite Newegg showing some their cards as PCI-E 2.0, all 5000-series cards are in fact 2.1.
So to correct my last post, it not read "majority," but should in fact say "all 5000-series cards are PCI-E 2.1."
The mistake is being made when sellers are taking descriptions from manufacturers which state the cards are "2.0 compatible," which all 2.1 cards are. But the interface is actually 2.1, not 2.0. That means there's always a compatibility risk when attempting to use them with 1.x boards.
As for the beta BIOS, it's certainly not readily available on their website. Renegade would probably have to contact them for it, or that guy on the HardOCP forums.