If you can only go for the 6950 then you should look at some benchmarks to see if the card will max out the game you want.You will have a hard time with BF3 on the ultra settings and that goes for both the 6950 and 6970.http://www.guru3d.com/article/radeon-hd-7970-crossfire-review/19
As you can see from the link the two cards will barely play the game at 31 and 33 fps. You need to go 580 or two 6950's in crossfire to get good smooth gameplay on ultra settings. Skyrim is a little different and not as demanding as BF3 so you will be able to use the 6950 on max settings and get good fps.
Do you have both games?