I have a 4,1 but haven't flashed to 5,1 mainly because everything I have is stock (except the RAM which is 1333 and meant to work with 5,1) and don't plan on upgrading CPU, etc. How is your 5,1 (previously 4,1) running macOS Sierra? I like to run Sierra, but it's not a "big deal" upgrade to me and I'm happy with El Capitan. I'm worried about possibly bricking my Mac Pro because I didn't flash it correctly. Btw, any danger of introducing vulnerabilities or malware by flashing? I'm also thinking of not flashing and getting the new iMac that's supposed to arrive sometime this year. But then what do I do with my 4,1 which is still running fine.