I upgraded from 10.10.5, had issues, subsequently have done several clean installs of 10.11.0 still have issues, with Apple`s own applications. Apple are simply pandering to the masses, I want stability & security first, 60 fps "buttery" smooth UI transitions are of no use to me if something as basic as Mail or Preview does not work.
Going to give it to 10.11.1 then will be rolling my Mac`s back to a working OS (10.10.5) IHMO 10.11 was released far too early in the development cycle. The worst OSX transition I have ever seen, I am of the mind that the less you use your Mac the more you will like 10.11, the more you use it, the more the OS & it`s bugs will interfere with your workflow.
When on the Keynote a new and "awesome" feature is the cursor growing if you shake the mouse, you know that Apple`s getting close to the bottom of the barrel...
FWIW this will be the first time I have ever considered rolling back OS X and that`s a long time...
Q-6
Still on 10.10.2 on both Macs...not even considering upgrading until the issues with MS Office are resolved.