Which OS X is the fastest?

Question

macOS

I have OS X EI Capitan 10.11.6 installed on a Mac Pro.
She is terribly slow. Even resizing windows occurs with some delay and jerks. Moreover, the more elements are in the window, the more it will slow down. Apparently, the operating system, when resizing the window, tries to redraw the whole thing on the fly, but it does not cope.
Please tell me the latest fastest and optimal system.
I read that OS X Mavericks was the last sane distribution of OS X, version 10.9.5

Answer 1

year of release of the poppy -> default version of the OS at the beginning of sales + 1 generation. No more.

Answer 2

On a macbook Pro mid-2010 with a dying battery (and we know that in this case performance is severely limited), Captain is noticeably faster than Maverick.