There are so many variables that can affect 4k performance it's hard to know exactly where to start from. All the other speeds look perfectly fine. As you said 4k can be changed by running on the OS drive, also the chipset you're using, SATA mode, chipset drivers. You can start with making sure you're using standard AHCI drivers, and ensuring your BIOS is set to AHCI mode. https://forums.crucial.com/t5/Crucial-SSDs/Replacing-Manufacturer-AHCI-drivers-with-standard-Microsoft-SATA/ta-p/176373 Otherwise test the drive in a different computer, if you only get low 4k results in this computer you know it has something to do with the chipset/drive combo, and it might be worth giving the board manufacturer a call.
... View more