High-speed memory kits are often associated with sloppy timings: Once you surpass that DDR4-4000 mark, it requires a lot of resources to cherry-pick the best integrated circuits (ICs) that meet the requirements. G.Skill is one of a handful of memory vendors willing to invest time and resources into bringing high-speed memory kits that aren’t held back by loose timings to the enthusiast market.

G.Skill offers a wide variety of DDR4-4000 memory kits with densities that start at 16GB (2x8GB) and go up to an awe-spiring 128GB (4x32GB).
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https://www.tomshardware.com/reviews/gskill-trident-z-royal-ddr4-4000-c17-2x16gb-review