USAFRet, He's talking about graphics, not system memory, mate.
Read the SLI/CF sticky at the top of the Forum, it's an old article now but still valid in most respects.
Me, I'd go for 1x4Gb if you're going to game on either more than one monitor or on a very high res monitor.
For a single 1080 display, a fast 2Gb card is still enough although you might want to consider a 3Gb card for future games.