At that resolution, the only bottleneck would be the cards themselves.
Try disabling shadows first and see if that helps. Shading in games causes the largest video overhead, even before resolution and anti-aliasing.
{edit}
As far as PCI-Ex 2 vs 3, your cards are most likely not filling the bandwidth of the current bus either way. Like running a 7200 rpm drive on SATA 2 vs 3... there's no difference because the drive's physical read/write speed maxes out before the bus speed.
Try disabling shadows first and see if that helps. Shading in games causes the largest video overhead, even before resolution and anti-aliasing.
{edit}
As far as PCI-Ex 2 vs 3, your cards are most likely not filling the bandwidth of the current bus either way. Like running a 7200 rpm drive on SATA 2 vs 3... there's no difference because the drive's physical read/write speed maxes out before the bus speed.
