Is DDR4-3600 CL16 the AM4 sweet spot? Zen 3 performance and timings

How this is calculated

1800 MHz bus clock, 0.556 ns per cycle, 16 cycles of CL = 8.89 ns. Per-channel bandwidth is 28.8 GB/s, tRC is 32.2 ns. On Intel platforms DDR4-3600 CL16 also works well, but the speed advantage over DDR4-3200 is smaller because Intel's ring-bus architecture is less memory-latency-bound than Ryzen's Infinity Fabric.

Verdict

At a 1800 MHz bus clock the kit lands on 8.89 ns first-word, faster than any stock DDR5 kit below DDR5-6000 MT/s, with tRC at 32.2 ns and per-channel bandwidth at 28.8 GB/s. The architectural reason this is the AM4 sweet spot is the 1:1 Infinity Fabric coupling: 3600 MT/s maps to FCLK at 1800 MHz on Ryzen 3000/5000, which is the practical top of where Zen 2/Zen 3 memory controllers hold the 1:1 ratio. Push past 3600 and you fall to gear 2:1, which is why DDR4-4000 CL18 actually loses to this kit on AM4 despite the higher data rate. On Intel the speed advantage over DDR4-3200 is smaller because Intel's ring bus is less memory-latency-bound than Infinity Fabric.