Well I updated recently. I haven't any big problems. Everything is working like before. However you can get problems with homebrew because of permissions. But there are easy fixes. If you have /usr/local just change the permissions.
If you were installing gems with sudo, you will get some trouble. The gems will not work anymore. But you shouldn't install gems with sudo no matter what. Change the path to your home folder and you're fine.
Couldn't see any performance improvement. Photoshop CS6 seems pretty slow. But I don't really mind because I switched to sketch a while ago.