I have 16gb, it wasn't even intended lul.
BetFenix Prodgy White - i7 - 4770K- MSI Z87I Gaming AC Intel Z87 ITX - EVGA Cooler - EVGA 780 - Samsung Evo 250 GB SSD - M4 128gb - Sennheiser px360 - Edifier R1600T Studio Plus 2.0 Monitors - AX860 Modular 80 PLUS Platinum 860W - ★QNIX★ QX2710 LED Evolution ll 27" PLS - Qpad MK-85 + G500
I asked this on another forum. Verdict is that it doesn't help games but can speed things up if you quickly tab out of the games while they're still running.
I had 4GB and was using 3.95Gb during BF3. Now have 8GB and can use up to 5.99Gb (I've seen) during BF3.
As BF3 itself is 32-bit (according to what I was told) it can only use 2GB itself anyway. It may help for running other programs alongside the game, but won't help the game.
And speed... utterly pointless with a fast CPU such as your 2700K!