Well, with a GeForce 8 series card, AA shouldn't affect performance as much and if it's a CPU optimisation problem then AA shouldn't affect it at all.
I've also got an E6600 and the perfomance seems to be a bit lacking here as well once I get above two full stacks, but I think I noticed it's a little bit better in 1.2. Some proper dual Core support would definitely be nice, but I doubt we'll get it before Empires.