oohhhh yeah. 8gb of RAM is plenty. If I needed more I'd buy it. I have never seen my system break the 6GB mark during BF3, but it reaches 5.8GB often. So, yes 8GB is the sweet spot.
Just make sure to get 2x4GB 1600MHz, not 1x8GB 1600MHz.
RAM is not that important in gaming, 4GB is more then enough these days.
8GB would make your rig future proof, more then enough for just gaming.
Only reason why i got 16Gb and probably going to upgrade to 32Gb is cause i use PhotoShop.