Yes, the short of it is that PCI 1.1 is equal to PCI 2.0 running at x8.
Thing is, most single modern GPUs still do not saturate a 2.0 lane yet, not even a GTX 580.
From the tests Ive seen, the only cards that start showing a performance hit at x8, are the Dual GPUs on a single card.
So running that card on a PCI 1.1 should not hurt anything at all.
The worst case scenario, you might loose 1-2 FPS, but I doubt it would even be noticeable.