I have two SN850 1TBs. One is installed to a PCH M2 slot, one to CPU M2 slot.
Both are reporting IOPS at around a third of expected.
I have a 980 Pro on another PCH M2 slot and that’s reporting better. Through Samsung Magician, that’s reporting almost 950k Random Read, 916k Random Write. The SN850s using the same app, a third of that and consistently so.
Sequential Read and Write are as expected.
One SN850 has 785GB free, the other 90GB free, out of 1TB per.
Running on MSI MEG X570 Godlike on BIOS 1.D3 (not the latest BIOS, I know).
Edit: Updated to BIOS 1.F4, no change.
Edit: Added screenshots of results.