Is DDR4-4000 CL18 worth it? Latency, Infinity Fabric, and setup guide

How this is calculated

2000 MHz bus clock, 0.5 ns per cycle, 18 cycles of CL = 9.00 ns. Per-channel bandwidth is 32 GB/s, 11% over DDR4-3600. The CL18 loosening almost completely cancels the data-rate gain, leaving a tiny 1% latency advantage over DDR4-3600 CL16, and only if the memory controller can run the higher speed stable, which many AM4 chips cannot.

Verdict

At a 2000 MHz bus clock the 18 cycles of CL lands on 9.00 ns first-word, only marginally better than DDR4-3600 CL16's 8.89 ns because the CL18 loosening almost completely cancels the higher data rate. Per-channel bandwidth is 32 GB/s, 11% over DDR4-3600. On AM4 the problem is structural: 4000 MT/s falls outside Infinity Fabric 1:1 range for most Zen chips, which drops the controller into 2:1 gear and adds enough latency that DDR4-3600 CL16 actually wins in real Ryzen benchmarks despite the lower raw data rate. On Intel 10th-gen+ the ring bus tolerates 4000 MT/s without that gear break, so the kit earns a small step up, but the price premium over 3600 CL16 rarely outweighs the slim performance gain.