Ok thanks guys for your feedback.
One question. If I look into my motherboard specs here:
https://www.msi.com/Motherboard/Z270-GAMING-M5/Specification
I can see: DDR4 MEMORY ==> 3800(OC)/ 3600(OC)/ 3200(OC)/ 3000(OC)/ 2800(OC)/ 2600(OC)/ 2400/ 2133 MHz
What does that (OC) means?! I know it is OverClock, but do they mean "it is overclockable" or that I need to overclock/modify a 3000MHz stick for it to work?! If I buy a 3000MHz RAM stick, will it be plug and play, or will I need to do something special?!