does having a ram speed of 2133 actually much better than 1600? is buying 1600 then overclocking it better than just buying 2133?
Overclocking RAM from it's stock speed can cause instability. If 2133 RAM is compatible with your system, buy that.
I recommend buying RAM that runs at the JEDEC voltage specs of 1.5v. Much of the faster RAM is nothing more than factory juiced RAM that probably wouldn't run at specified speeds at 1.5v. RAM speeds should be matched to the CPU as well as the motherboard.
We need to know which CPU you have & the make/model of your motherboard.