|RAM choice depends on the motherboards specs & which CPU you're running. Here's the memory support specs according Asus:|
2 x DIMM, Max. 8GB, DDR3 1866(O.C.)/1333/1066 MHz ECC, Non-ECC, Un-buffered Memory
Dual Channel Memory Architecture
* Refer to www.asus.com or user manual for the Memory QVL (Qualified Vendors Lists).
* Due to OS limitation, when installing total memory of 4GB capacity or more, Windows® 32-bit operation system may only recognize less than 3GB. Install a 64-bit Windows® OS when you want to install 4GB or more memory on the motherboard.
* AMD AM3 100 and 200 series CPU support up to DDR3 1066MHz.
I recommend 8GB (2 x 4GB) DDR3-1600, CAS 9, 1.5v. And you will need to install a 64-bit OS. Here's one possibilty: