We have 2010 Macs capable of being upgraded to macOS Sierra in my office. I couldn't tell you about the 2009 Macs as we upgraded anything that old some time ago. However, at the moment we are running OS X El Capitan due to the main software we use to run the patient data base has not been certified yet to be reliable on macOS Sierra by its publisher as well as the 3D radiography software has yet to be upgraded. So we wait.
Those 2010 Macs are scheduled to be replaced next year, though. They've done their duty for six years.
I have a couple 2009 Mac Pros running Sierra. Biggest problem is bluetooth and wifi, one of my macs had been upgraded the other I had to use a USB bluetooth to get to bluetooth 5. Of course they both had the software hack installed to make the machines report as 5,1.
I managed to get “Sierra” on my “Early 2008 Mac Pro” tower...it is called “vintage/obsolete” now even when it’s GeekBench score is about 12,250...better than a lot of “current” Macs/PC’s (24 gigs RAM, 8 core Xenon, SSD).