Without familiarizing to the bunch of variables:
3 GB should be enough for AH3. There's been reviews, though, that the seemingly minor differences in the design (other than the amount of memory) can cause surprising hiccups in games. However, that might have been an early driver issue as well.
Two fans might mean lower rpm for the same cooling effect which means less noise. Two fans might also spread the airflow more evenly.
Overclocking by, say, 10% is barely noticeable. It might make a difference if you get from 28 to 31 FPS, but not that much from 54 to 60.