Both the high-end and mid-range platform from Intel support DDR4, AMD is set to follow suit this year. High time to compare a good amount of sets: what do you need to keep in mind and which should you buy?
Halfway 2016 was the ideal period to purchase memory modules: DDR4 was never that cheap before. Unfortunately the prices have been rising ever since. 8 GB was the standard for the average gaming PC for years, however 16 GB is not an unnecessary luxury if you're building a PC right now, if you take the future into consideration. Video editors and other demanding users will benefit from 16 or even 32 GB anyway.
Is faster memory actually useful?
The last couple of years you'd mainly be advised to buy lots of memory, disregarding the speed of said memory. The only exception to this rule were systems with an integrated GPU, as it uses the RAM as its video memory. Otherwise the performance differences were basically non-existent. Recently benchmarks have popped up on the internet that showed that Intel's sixth generation (Skylake) of processors does indeed benefit from faster memory. Of course we tried to replicate those results, since that would change the memory market considerably.
We found performance increases of up to 10% in certain games, that were mostly achieved at lower settings. This is because you don't have any GPU bottlenecks in such a situation. In general we only see improvements though, so spending a bit more for a faster memory kit seems justifiable. Heavy CPU tasks such as video-encoding have always benefited visibly from faster memory. If you absolutely have to choose between more or faster memory, we'd still recommend the former.