This is one of the responses I received:
"There were issues with the card - especially with classic Mac Pro Tower users and Sonnet pulled the current stock pending a re-work last month (late Sept. 2018). They now have new cards with a serial number beginning with 'B' (so they are Rev. B). This is information from Sonnet Support. I hope to see more positive reviews coming in pending their re-work was successful."
Hi. Curious if you still have this setup and if it is still working well with the Sonnet Solo 10G PCie? Recently upgraded my Synology NAS which has 10 gigabit capability, and looking to upgrade to 10G speeds on my Mid 2010 Mac Pro 5,1 as well. Thanks!