Introductory note

Memory is most blatant ripoff among all products related to computers.

All, 100% of so called "gamers" or "overclockers" memory is based on same 2133Mhz or 2400Mhz chips as cheap DIMMS.
Higher frequency chips are just selected among specific manufacturing batches aka dies. And sometimes not even tested properly (to save funds).
For manufacturer main expenses for such kits lies in the bigger competition for select chips (can be up to $10 extra for 8GB DIMM), around $1-3 they spend on fancy alu heatsinks and $1-5 they spend on more colorful packaging. All else goes to pure profits, marketing expenses (can be large for small manufacturer), distribution and retail parts.

Yet for many modern CPUs memory speed and timings greatly affect overall performance. And with each year such dependency increases due to lack of real progress in DRAM technologies. You can thank big patent troll named Rambus for lot of today issues.

Male sure to check https://www.personal-view.com/talks/discussion/19652/short-ddr4-memory-guide-for-video-guys