Depend on the sticks and what you do, most people just look and see 1600 - 1866, but need to look into a combo of the freq, say 1600 and the CL (the first number of the timings), the CL in effect is how many clock cycles the DRAM takes to perform an action....... so if you have 1600/CL7 it can do something in 7 cycles (relate a cycle to a timed second) or 7 seconds while 1600 CL11 would take 11 seconds for the same action....the difference in the freq is how many MB the DRAM can process within that perior with 1600 it's theoretically 12, 800 while 1866 is 14,900 so effectively 1600/9 is just a bit slower than 1866/10.....but 1600/8 would be a bit faster that 1866/10