So over in the OT section we were talking about the effects of gaming on 4GB and 8GB, specifically in BF3. This perked my interest up as I'm currently running a "run of the mill" CPU, and so of course I decided to do some testing.
Each test is done on the same 64 player server with 64 players on it. The map is Canals and the game type is TDM. Each test is done at stock settings. Stock CPU, stock GPU, stock RAM both at 1600MHz 9-9-9-24 timings. I had everything I normally run in the background going for each test which is Xfire, Skype, FRAPS, Origin, and Chrome (typically with Gmail, Facebook, and Battlelog tabs open) just for some background action. Each test I record FPS for 5 minutes.
As we can see, not much of a difference. Reason being, BF3 doesn't take that much RAM to begin with so the only reason you would need more RAM is if you have a ton of junk running in the background. If you have performance issues, this would be why.
Please realize, not every test done is going to be exactly the same due to the nature of MP. This is as realistically possible I can get to benching BF3. Small map, lots of people, tons of explosions and gunfire.