If you can get reference design 6950 there is a high probability you can flash it to 6970. I have done it it is easy. I run 2 in CF. However I got 2 more for my wife's comp and these were nonreference design and I was unsuccessful in flashing it to 6970.
Anyway, I would go with 69501gb. If you want 560TI go for it but you don't even notice Physx in games.