In Nvidia's Camp Id go Either 660, 660ti, or 670
In AMDs either 7870 or the 7950
All the games you mentioned, besides FC3 and AC3 (Dont own them) run maxed out with 2xMSAA or High FXAA at 1920x1080 with 60+ FPS on my GTX 660.
Only thing I have to turn down sometimes is Tessalation in certain DX11 games.
(Best CIV GPU EVER! MAXED)
Just my personal opinion mixed with some actual facts =D