What does CPU-Z memory tab tell you?
It should say 1200Mhz if set right (then times by two as its DDR).
Memory (RAM)
Size16384 MB
Type DDR3-1333 - Dual Channel
Frequency 666.5 MHz (1:5)
Timings 9-9-9-24
Slot #1 ModuleCorsair - 8192 MB (10700)
Slot #2 ModuleCorsair - 8192 MB (10700)
Its 1200x2 = 2400Mhz.