for that motherboard, you must enable O.C mode (manual timing) in bios to unlock the 1866 speed you want.
then ENABLE "X.M.P" profile in bios and it will set the best timing and voltage for your memory at 1866 spd for you, no guess work.
google "xmp memory" for more info
ASUS P8Z77-VLK, I5-3570k @ 4.4ghz, G.SKILL 16gb 1600, GTX 570 2560MB GDDR5, 2x OCZ Vertex 4 128Gb SSD SATA 3,
WD 500GB SATA 3, ASUS DRW-24B1ST SATA 3, OCZ ModXStream Pro 700W Modular, Samsung 52" lcd, Win 7 Ultimate x64 SP1