Please help me decide

Hello,

About 4 years age i bought a PS3 and since then i never touched my pc for gaming. But now i miss rts and want to play on my pc again. It is only stratagy i want to play because shooters make me sick (literally).

The games i want to play this year are:

Anno 2070
Tropico 4
Cities XL
Skyrim
Starcraft 2 ( the reason i go back to pc )
And Generals 2 next year.

So now i have the option to buy:

2 x Sapphire HD 6850 2GB for a total of 320 euros
2 x Sapphire HD 6870 1GB for a total of 298 euros
1 x Sapphire HD 6970 2GB for a total of 294 euros


Please can you give some advice. I know nothing is to say about Generals 2 but i guess al option above should be enough...