So, before I will go to RMA and ask for Samsung NVMe, I wanted to test, what's wrong with Toshiba NVMe we have in Inspiron 7577. I thought it can be faulty, or whatever, but hats to Dell/Intel/MS/Toshiba I guess. Without any drivers, as I can do that with Windows 10 LTSB 1607, just disable all **bleep** MS wants to put to my throat, speeds are fine, as advertised.
I still didn't tried to install Intel Chipset or any other drivers, except graphics and audio - Intel HD and nVidia. I will try Intel Chipset later and I will see, if write speeds, including just copying files in Windows (Max was about 800 MB/s), will be as usual - 350 MB/s.
download the OCZ (Toshiba) NVME drivers ie. mod+signed drivers 64 bit
Follow the instructions on page 1 to install the driver but you must extract and run the certificate copy bat as an administrator or else it won't copy. If it doesn't copy installation of the drive will fail.
Install the updated driver as per instruction and reboot.
CDM was giving me high 900's on my 7577 i7 rig
Copying from a samsug T5 USB-C External SSD was going on at 400MB/s at it's slowest.
It is still slow to copy from the internal HDD to the NVME drive but I think that is jus a limitation of the spinning disk.
Made the world of difference, not my work, but I hope it helps.
Credit to<Email Id Removed>
I tried your solution, but same - speed goes down after a while too 350 MB/s. I also tried new firmware from Dell site, still the same.
No probs, sorry it didn't help you. Mine is much better now but still far from Toshibas posted speeds.
One day they will release a driver, one day.