I was looking into cases for my new 6950 as it wouldn't fit in my old case (NZXT Alpha). The NZXT Gamma was one of the cases I was looking at (before I found a good deal on an Antec 300). I did find some forum posts saying people were able to put the 6950 into the Gamma. Let me see if I can find those posts again.
Also, all 6950 2GBs are reference length right now, which should be 10.6 inches.
Also, unlike the older 4870s, the power connectors are on the top of the card, not the rear. (The rear connectors were an issue in smaller cases where the HDD cage obstructed the connectors)
Edit: Here's one poster on overclock.net
water cooled NZXT Gamma pics - Overclock.net - Overclocking.net