When Windows 10 was reinstalled, what version of Samsung Magician currently installed?
I have tried 5.3.1 - The scan takes much longer than v4, but still same result. i went back to 4.97, it does disk tests twice as fast.
To see if your observations can be recreated, are you using benchmarking software other than that within Samsung Magician?
Which File System is the Windows partition formatted to now? NTFS/Default
Is the installation using Samsung Magician's Over Provisioning feature? No. It did on previous windows version, but it didn't make a difference.
What is the firmware version of the 850 EVO? Is the SSD firmware up-to-date? Latest EMT02B6Q
Is Samsung Magician's RAPID mode enabled? Rapid mode wacks all results out of proportion, i have it disabled right now until this this is sorted