1333 (16x2GB) 9 cas or 1600 (4x2GB) 8 cas

[jaeiiijae]

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231445
G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL8D-8GBXM

OR

http://www.newegg.com/Product/Product.aspx?Item=N82E16820233296&Tpk=cmx16gx3m2a1333c9
CORSAIR XMS 16GB (2 x 8GB) 240-Pin DDR3 SDRAM DDR3 1333 Desktop Memory Model CMX16GX3M2A1333C9

 

[alexoiu]

IMO, it depends on:
-what applications running mostly,
-motherboard and CPU.