100 usd is not a problem for me. If i am not gonna have bottleneck with e8400 @ 3.8ghz , then will be buying 2gb version of 6950 and flashing it to 6970, otherwise will get the 6850.
Well you will have bottleneck, but it won't be that bad because your E8400 is clocked to almost ~4GHz. Besides, any game out there will be playable, it's just that the card won't show it's full potential with that CPU.
And you'll be buying a new platform for 1-2 years, right? So the HD 6950 2GB is overall a better choice, especially if you flash it to a HD 6970.
2xHD 6850's in Crossfire are going to give out some better performance at a 70-$80 lower price. It's not worth it, and he'll have more bottleneck problems with that card, because 2xGTX460's=GTX580. 2xHD 6850 are somewhat better than the GTX460's as i already said, so his only option for a high end GPU with that CPU is the HD 6950 2GB.