Yes,
I upgraded my HP z800 bios to the latest version. I had Windows -7 installed and I downloaded the latest bios update and extracted the zip file and then ran the HPQflash.exe . reboot and your good. I run Windows-10-Pro today.
z800 Works Great with Windows-10 !.....
http://h20564.www2.hp.com/hpsc/swd/public/readIndex?sp4ts.oid=3912036&swLangOid=8&swEnvOid=4059
I am using a Samsung Evo 850 SSD with PCIe adapter ( Works good )
SSD benchmarks are 520mb/s read and 505mb/s write.
PCIe Adapter
https://eshop.macsales.com/item/OWC/SSDACL6G.S/
Samsung SSD