Leaderboard

Yep! Since ZFS uses RAM for caching, more RAM means more cached data which means faster retrievals. Compared to the bottlenecks like 1Gb networking, HDD speeds, etc, RAM speed shouldn't be very impactful.

Concerning question 1: Nowadays, the memory controller is baked into the CPU, so the CPU defines the supported Memory speed and quantity (mainly). In this case it is the 2666 which was mentioned and since everything higher then this is considered overclocking, and a lot of H370 boards don't support overclocking, that's why you are likely limited to this speed. Some Mid- to High End H370 boards support overclocking but I doubt that an OEM board does. Therefore, don't go with faster RAM and take more RAM instead.

before i built my server i did a decent amount of google searches to see if faster ram makes a difference. Pretty much everyone just said to focus on more ram than faster ram.