Don't matter what slot you install, a non-switched card will always be limited by PCIe 2.0 4 lanes = ~1500MB/s.
You should go to the first post and read it, it's already answered there.
Hi Tsailex
I'm contacting you because you seem to know what you're doing. (a shortage of these types these days)
(I really don't have the to read tech boards these days)
I purchased the highpoint ssd7101a and the samsung 970 evo in a 2 gig capacity.
I wish to perform a FRESH INSTALL of Sierra into the samsung 970. (not High Sierra or Mojave because I have too many apps which will not function)
Unfortunately I just haven't the time to read reams of info on this and some of the stuff I have seen seems overly complicated involving installing multiple third party software applications and many many step backing up ROMs and "injecting" code.
I have a mac pro from mid 2010 which has been upgraded to a 12 core 3.46ghz machine. It is currently on Sierra 10.12.6
Mac Pro
Model Identifier: MacPro5,1
Processor Name: 6-Core Intel Xeon
Processor Speed: 3.46 GHz
Number of Processors: 2
Total Number of Cores: 12
L2 Cache (per Core): 256 KB
L3 Cache (per Processor): 12 MB
Memory: 64 GB
Processor Interconnect Speed: 6.4 GT/s
Boot ROM Version: MP51.007F.B03
SMC Version (system): 1.39f11
SMC Version (processor tray): 1.39f11
Serial Number (system): H00511KHGWR
Serial Number (processor tray): J5045011LBH8B
Hardware UUID: 43FD3FC3-A2A3-554D-8FA5-53B8F39FA1E4
I have an Nvidia Tiitan XP installed and working.