I was just looking at 2133Mhz RAM and noticed most of them have a CAS of about 11 as the cheapest. I know this will mean longer delays between the RAM Refresh Cycle but will it really affect my FPS. For reference, I do plan on Overclocking my CPU and the iGPU.
You need to realize that CAS is just as important as the more "screaming" Mhz number. For example 2133 Mhz memory with CAS 11-11-11 is actually slower and more expensive (dumb, but well, people are not very smart either) than 1866 Mhz 9-10-9.
As a matter of fact, unless you are FILTHY rich - best memory would be 1866 9-10-9.
Besides that, though - there is nearly 0 impact on FPS in reality unless you use iGPU, which I hope you do not. Differense between an okish standard memory and roflbbqrotschild memory is about 1 FPS.