If this has been addressed before I apologize - I couldn't find it.  I have a 4,1 w/ firmware update to 5,1.  Running Sierra and Maverick.  I did do the 1.4 update to be able to run nvme bootable as I was running High Sierra with an Sapphire Pulse RX580 but moved that setup to another MacPro.  So, I put my old 5770 video card and my ssd with Sierra back in and everything is fine.  I'd like to go to a raid 0, nvme setup for the fastest possible speed to do audio recording.  Bottom line, which pcie card is best for running raid 0 with nvme as the bootable drive?  Since I updated to 1.4 firmware will Sierra and Maverick both be able to boot from nvme?  How much speed gain will I expect to see with nvme in raid 0 versus a single nvme drive.  I'm hoping, if this setup is even possible, the expected speed gain from raid 0 nvme will outweigh the risk associated with raid 0.  I am somewhat confused by all the posts I've read about nvme speed increases, boot capability, pcie bus speed limiting the nvme, etc.  Hope someone can clear up the confusion so I can get what I need ordered and up and running.  Love the forum, thanks for any input.