3200MHz seems to be the sweet spot based on cost vs performance.
Coffee Lake Memory Benchmark Analysis, performance gains to be had when going up from the reference 2666MHz to 4000MHz. https://www.techpowe...hmark_Analysis/
However if you were to ask me which is more important: speed or latency?
Based on my own testing, gaming at 1440P/4K,.. the answer would be speed.
In general, as speeds have increased for Z370 chipset, true latencies have remained approximately the same, meaning faster speeds enable you to achieve a higher level of performance.
True latencies haven't necessary increased, just CAS latencies. And CL ratings are an inaccurate, and often misleading, indicator of true latency (and memory) performance.
Edited by Braegnok, 13 September 2018 - 06:07 AM.