960 and 970 are both much faster, capable of 3200+ MB/sec sequential reads, vs. ~540 MB/sec of the 850/860, regardless of chosen form factor of the latter pair (standard 2.5" SATA or M.2 SATA, both capped at ~550/MB/sec)
NVME drives are much faster on paper, but, the difference for gaming is not as noticeable, perhaps a second or two shaved off of gaming load level times (24 seconds vs. 26, etc..), and a few seconds saved on bootup/shutdown, and MUCH faster total installs of OS, if ever required...(I was able to install Win10 Pro from USB to 960 EVO in about 4 minutes or so...)
They are worth the extra $100 expense, but, never compromise on CPU or GPU to afford NVME over a standard SATA, IMO....