As a comparison, I'm running a 15TB mdadm ext4 array on the following hardware:
EPYC 7443P 24-core CPU
256GB 8-channel RAM
8x Samsung PM9A3 Gen4 NVME U.2 1.92TB drives, connected via 2x AOC-SLG4-4E4T-O bifurcation re-timer cards
Seeing ~40GB/s read and ~20GB/s write via a sequential FIO test.