I'm running 10.11.3 on my 2009 Mac mini (2GHz 8GB) and it's just got too slow. I'm seeing the beachball way too much. I want to downgrade to an older version of OSX to get some speed back. How old should I go? If I could definitely remember which iteration of the OS was the last to run at an acceptable speed I'd just go there, but I can't. But I've got a vague idea that I started feeling that things started to slow down with Mavericks. So I'm thinking Mountain Lion... any major reasons why I shouldn't?