I have the 1TB SM961 in my R5E and use it so far as only my Windows drive (though Star Citizen is also on it).
Pros:
1TB
Looks nice (i.e. you cant see it hidden under a graphics card), makes for a clean windowed case build
Fast
Temp monitoring in AIDA 64 works.
Doesn't get that hot at all when used mainly as a "read" i.e. boot drive.
Cons:
Samsung Magician software won't recognize it so you will never be able to update the firmware
However, Samsung never even issues firmware updates for the OEM drives away.
Magician Pic:
a quick bench:
*CPU: Intel 10980XE @ 5.0 ghz (by Core usage) w/ EK monoblock
*Mobo: Asus Rampage VIE
*RAM: 64GB DDR4 3000 G.Skill TridentZ
*Graphics: Gigabite 3090 Waterforce
*Monitor: Dell Alienware AW3418DW @ 120hz
*Storage OS: Samsung SM970 Pro (2TB) Windows 10
*Storage Games Internal: 4TB 850 EVO RAID0
*Storage Extermal: 48TB Raid0 (External USB 3.1 Box)
*Case/PSU: Thermaltake V71 TG/RGB + 3 Rads (120mm, 360mm, 420mm) + Corsair AX1200i PSU