Which RAM is suggested

Hi there, I want to upgrade my RAM to 16 GB and not sure if I can use 1866. The manual says supported RAM is
4×240pin DDR3 1866(OC)/1333/1066
*To reach DDR3 1866MHz or above, you must install two memory modules and install them in the DDR3_3 and DDR3_4 memory sockets.

My sys is :
Mobo: GIGABYTE GA-870A-UD3 AM3 AMD 870 SATA 6Gb/s USB 3.0 ATX AMD
BIOS: AMD 870 BIOS for GA-870A-UD3 F2
CPU: AMD Phenom II X4 965 HDZ965FBGMBOX
RAM: OCZ3SOE1600LV4GK
Vid: XFX Radeon HD 5770
PSU: stock with Sonata III case
HDD: Western Digital Caviar Black WD1002FAEX 1TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5"
OS: 64 bit Win 7 ultimate

thx in advance