If you have it may as well use it. That's assuming you are using Windows 7 64. If you're using XP then 4 is the max. (or is it 3.5?) I was running 4GB for a while on my new win7 machine as I was troubleshooting an issue and had taken out all but one stick. I found it quite tight. I'd often get low memory messages, especially when using autocad, photoshop, UT3 editor and other apps of that nature. 6GB will give you that extra buffer, 12GB will give you even more buffer.