What Suzterra said above. Either card will simply run at PCIe 2.0 bandwidth. This definitely isn't a problem, as even the faster cards out there can't even full saturate half of a full PCIe 2.0 slot
At the same price or cheaper, I would have to give the edge to the R9 280. It has more VRAM, and performs similarly, if not a tad better than the 760.