Advice sought please - Mac Pro PCIe mounted Samsung AHCI SM951 Blade shows dismal write performance using Black Magic Free Speedtest… about 200 MB/s vs the read of about 1400 MB/s..

Tried allowing all the permissions on this PCIe Slot 3 mounted Samsung SM951 AHCI disc's boot OS, from different accounts, from another OS X with Yosemite 10.10.5 on it, tried SMC & PRAM resets.. removed all 6 other internal discs and the attached NAS, all the peripherals… went (right) back to a wired mouse/keyboard & 1 screen...… still can’t loosen up the permissions… pretty certain this is why I have a really really slow computer whenever some ‘writing’ is required (which is all the time)...

All Black Magic Free Speedtests show normal, thats internal SSD'd mounted in PCIe Slot 2, Internal SSDs mounted in the DVD Trays and SSD's & HDD's in the 4 Sled Trays etc.. it's just the one type of disc that I cannot get working properly, it's now the primary boot disc, with OS X High Sierra 10.13.2... it's a 256GB and runs about half used/half empty mostly...

It's the 1st time, and only time, that I have a disc I can't unlock all the permissions on, so thats my 'Guess #1'.

Pictures probably speak a thousand so...