1. You probably won't see a big dif between the 6950 and 6970 in games.
2. If you want extreme OC, the 6970 is the way to go.
3. Some people have issues with the flashing, and I can't find anything on the Frozr card specifically. Can't guarantee it.
If I was you, I would either get the 6970 right off the bat, or get a good 6950 and OC the hell out of it.
I believe the consensus generally is that 6950 is the way to go because it is so close to being the same card/performance of 6970 and for over $100 less I would have to agree.