I use my Mac for business, meaning I need really rock solid stability, not fancy features. There is nothing in the El Cap feature set that I need for business. The single and only reason I would upgrade is to keep the Mac current with software apps that I will need in the future. Question: which do you find is more stable -- Yosemite 10.10.5 or the current El Capitan 10.11.3 ? With Yosemite, I note a "bug" where it can take ages for the Mac to connect to our server via networking. Sometimes it does not connect, so I have to stop using the Mac and revert to a Windows computer to connect to our server. I read that this "bug" has existed for quite a while, and that Apple have never adequately addressed the problem. I'm deciding whether to upgrade from Yosemite to El Capitan, hence the question.