Well my question is, is this upgrade really worth it? I game 1080p. Skyrim, Battlefield, Diablo, LoL, FarCry 3 etc...
To a 660 no to a 660ti or 670 yes also make shure your cpu does not bottleneck the 2 gpu's I listed before If you do go for them
No, a 7850 to a 660 would be a very small upgrade. Go for something like a 7950 or a 670 if you really want to upgrade, but I'd suggest against it since the 7850 is still a really good card
A 7850 OC'd is faster then a 660.