^ Hold your horses!!! - Any AMD MOBO is a Dual/Quad Channel MOBO so everything is in PAIRS.
4GB (2X2GB) and the speed is based upon what's supported by you MOBO. In general 1600 MHz is the 'normal' for most OC.
You do NOT want to get a Tri Channel kit!!! In addition, before buying any memory: 1. Goto the MOBO website and look for Certified RAM, or 2. Goto the RAM Mfg website and use the RAM CONFIGURATION tools to look for Tested RAM.