You are asking the wrong question, or, really, not asking enough questions.
Do you mean how much will the memory overclock - 5%, 10%, 50%?
Do you mean to what speed will the memory overclock - 2800 MHz, 3000 MHz, 3400 MHz?
How much any memory will overclock (percent or actual speed) depends on what ICs (the little black squares) are used on the sticks. Some ICs will overclock much better than others. And it's difficult to find out what ICs are on memory sticks until you buy them, remove the heat spreaders and read the codes printed on the IC themselves.
It's actually much more complicated than the above:
If a memory manufacturer want to build and sell 100 sticks that will have a 2800 MHz specification he buys ICs that the IC manufacturer says will do that and builds the memory with them.
Then the manufacturer tests all the memory he has built
Out of the 100 sticks he has built 4 may only run at 2400 MHz. He puts those in the 2400 MHz bin
Out of the 100 sticks he has built 90 may only run at 2800 MHz. He puts those in the 2800 MHz bin.
Out of the 100 sticks he has built 6 may only run at 3000 MHz. He puts those in the 3000 MHz bin.
This process is called "Binning" and all memory manufacturers do it. Of course the 2400 MHz memory is worth less so he sells it for less than he sell the 2800 MHz memory, and the 3000 MHz memory is worth more than the 2800 MHz memory so he sell it for more that theb2800 MHz memory.
Sometimes, for various reasons, a manufacturer way sell higher binned memory and give it a lower speed specification.
Perhaps he needs 2400 MHz memory for one of his customers, but only has memory that binned at 2800 MHz on hand. He will take the 2800 MHz memory and spec it's speed at 2400 MHz just to be able to supply the customer.
Generally memory won't overclock very much unless the binning process is not followed for some reason or another. When that happens, and it rarely does, some fantastic memory hits the market!
So where does really, really fast memory come from, like 4000 MHz
? The memory manufacturer may have the ability to bin the actual ICs he gets from a manufacturer. Out of thousands of ICs a few may be able to run at that fantastic speed. The manufacturer puts them aside and one day, when he has enough of then, he may build 25 4000 MHz sticks and sell the for a fantastically high price.So, basically your best course of action is to buy the fastest memory you can afford and hope to be able to overclock it a t least a little bit.Edited by billbartuska - 4/11/16 at 9:34pm