I have had no issues with my 8x since the update, mine shuts down and reboot in 1 min., battery improved a lot., no wifi problems.
I just made sure that , what I like to call back ground nose, is shut off ( news, face book, auto updates on apps, ect.) they all take resources from your phone, and slow it down, or when shutting down the phone all that stuff has to tune off which take time. then on reboot its turned back on. they update anyways when you visit the app. so shut them down and see if it improves your performance.