You can have a look at THIS. You can also google memory benchmark and get loads of programs, like everest, that will give you idea of how fast your memory is running. I really don't think you will be able to tell in day to day use if you have 1600 or 1866 setting either to their lowest clock settings and both at 1t.
It depends on the task you are doing. If you're doing one continuous task for maximum speed, then 1866MHz is better. If you're doing more, smaller tasks, the lower latency of the 1600MHz RAM is better. Personally, I would choose the 1600MHz with 7-7-7-2X timings. My RAM is rated for 7-7-7-24, but I can run 7-7-7-22 1T @ 1600MHz or PC2-12800. I hope this helped.
Alright, after hearing a few opinions here it seems that most of you can agree the lower timings at 1600 are better overall than the higher timings at 1866. As of right now I have left it at 1600 with the lower timings (7-7-7-20-59 rest auto, 2T).
If anyone else can chime in I will still appreciate it..The more opinions I get the more reliable the decision I make
1866 @ 9-9-9, command rate 1T
1600 @ 7-7-7, command rate 2T
Which is faster?
ps: Don't worry I will choose a best answer soon.. I just want to see if anyone else has anything to add for a couple days and finalize my choice!
There is an interesting sentence at the conclusion of the article:
"The results are obvious: going from one memory speed to the next, e.g. from DDR3-1066 to 1333, does not provide major benefits. Even the replacement of slow DDR3-800 RAM by DDR3-1600 memory will mostly yield disappointing results. While the performance advantage is measurable, it is never noticeable."
I think performance-wise you will not notice any differece at all between the two settings, but I'd probably go for the lower latencies.