Tradesman1 :
I'd suggest a 2x2GB set so you can utilize dual channel (up to 10-15% performance increase over single channel)
A 2x2 set is never a good reccomendation. Because later on if you want to upgrade to more it is so very limited over a 1x4gb stick.
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While not my favorite (2x2GB) it's better than a single stick because you can enable and use dual channel which provides a performance increase as mentioned, that particularly good with AMD rigs as they havea weak MC 9Memory controller) anywayway, as far as upgrading - You don't want to mix sets or sticks of DRAM in the first place, it can be problematic, and even moreso on AMD vs Intel due to the weaker MC - it's always best to get a set of the full amount of DRAM you want, and if need be sell the old or use it in another rig