From my experience, the RAM speeds won't change your performance a HUGE amount. However, if you are like most of us, assuming that your on OCN you are, you are wanting to get everything running close to, or at its optimal level of performance.
Therefore you do want to get a decent set of RAM.
My theory is this. DDR4 will still be around for a while, at least another 3 years. I may upgrade before then, I may not. Who knows.
I do know though, that if I do upgrade, I don't want to have to touch my RAM.
Also seeing where AMD is going, if I do upgrade it will be AMD. Based on that assessment, ram timings at decent speeds are more important than flat out speed.
So I went with a fairly high end set of Samsung B-Die, and i could not be happier. I got a 3200 C14 set, and am currently run at 3733 C16 and have not tried tightening timings yet, so I could improve that a bit more.
B-Die is just really really great RAM chips. End of story. Everything else is trying to get there, but just cannot.
So i vote getting a set of B-Die RAM