So I've decided to give it a try. I have a late 2015 M390 iMac. And I was having too much UI lags. Specially when switching Spaces. Mission control was working like a Slo-Mo movie. I'm happy to say that my iMac is now running like it should. Fast, hell fast! My complains about UI were gone. Mission Control now works fine. That's another little thing. BT was dropping connection constantly, just half a sec. And everything just connects again. Now, since the 6th deliver it's working fine, no more drops. You guys should try it. I'm in love with my iMac again!