What's the FASTEST version of macOS for my Mac?

I produce music with Logic Pro and I want to have the operating system with the best performance for my iMac. I used to run OS X El Capitan on a Mac Pro (trashcan) but when I upgraded to Catalina it was painfully slow, so I sold it and bought this:

I have held off upgrading the OS because historically, my experiences have resulted in loss of performance and I fear that all the new modern features will slow down my workstation. However, I recently read an article suggesting that Big Sur is optimized in a way that could give a performance boost on SOME machines and I'm wondering if my Mac is one of them.