Thank you for all the suggestions. I followed up with each one carefully.
My motherboard supports the following M2 slots:
2 x M.2 Socket 3 connectors (Socket 3, M key, type 2242/2260/2280 SATA & PCIe x4/x2/x1 SSD support)
My M2 can be connected in either of these 2 M.2 slots on my motherboard:
Dual PCIe Gen3 x4 M.2 Connectors with up to 32Gb/s Data Transfer (PCIe NVMe & SATA SSD support). The motherboard instructions say:
The PCIEX4 slot shares bandwidth with the M2H_32G connector. The PCIEX4 slot will become unavailable when an SSD is installed in the M2H_32G connector. I tried both slots just for the hell of it, but noticed no difference.
x4 is turned on in the BIOS (x2 wasn't even an option) for the M2 slot.
I'm not sure how to test for a heat issue.
CrystalDiskMark seems to be showing accurate data, compared to Samsung Magician which appears to be wildly inaccurate:
970 EVO:
850 EVO:
Is CrystalDiskMark the trusted source here? Maybe Samsung Magician just has a bad speed performance test tool?