2 Gb of memory would get you increase in performance.
2 gb will give you absolutely NO increase in performance over 1gb, in 3dMark anyway.
There are very few games out there that care if you have 2 gb. Doom3 doesn't care. Half-Life2 doesn't care. FEAR doesn't care...
Battlefield 2 is one of the very few titles that will utilize 2gb of RAM.
Maybe 2gb would decrease your load times (which is nice)... but your framerates would not jump one iota.