vapour :
Nah, ram speed is independent of CPU overclocking afaik. You can OC them separately.
Of course you can, but it won't actually improve the system's performance in practice. CPU and RAM communicate and exchange data, so if RAM is much faster than the CPU there is no actual gain.
You can also buy DDR4 RAM with an effective clock over 4000 MHz, but it's probably a waste of money if you are going to combine it with the i3-8350K that you haven't even overclocked.
I think you get my point and the meaning of my question.