Out of interest - what computer did you do the sustained copy on? As you were seemingly getting up to 3.5GB/s write on some of the test machines, but the initial copy on the sustained 142GB write only achieved 1.3GB/s.
Dropping to 800MB/s after only 52GB copied (1.3 x 40) is somewhat disappointing, many modern Nvme drives manage almost a 1/4 of their capacity in pSLC cache.