Thos are nice cards and all, but I don't have a PCI 3.0 Board.
Neither do I and I run a GTX680. It is backward compatible. Those cards will not come close to saturating the bandwidth of a PCI-E 2.0 x16 slot.
I should also ask which Antec 550w PSU you have. I am sure it is fine, but always good to double check.