I know it's a huge pain and nightmare to do a full, hard reset but it worked for me. If there was a problem after the update, I was having it. Battery dropping like a brick off a skyscraper, Google process error, slow response, call quality, it was horrible.
The past week since I got the update I have been kicking myself for installing it and hunting forums to find a way to fix it. As a last ditch attempt before I rolled up in the store to rip into someone, I decided to wipe it clean and start again.
First I had everything backup to google and took screenshots so I could put everything back in it's place that I'm used to. Then I connected to USB to get all the music and pictures off. When I did that I noticed it was filing them out of correct folders. Music was a bit out of place as well... I got it all moved to my laptop and organized correctly again, but it was weird. Then I did it, hard reset.
The second odd things after the media in odd folders was, a couple apps wouldn't reinstall. Since they were already installed prior to upgrade, KK didn't delete them after the upgrade. After the reset, I couldn't install them again so I think that may be some of the problem as well. They were prolly trying to run, which bogged it down and sucked the battery so fast. But anyway... ALLLLLLL problems fixed. It's faster, the battery seems to be lasting longer than even before the update, fast responsiveness and I am back to loving it.
I'm not saying this will fix everyone and everything... I just thought I would share because I have been searching the internet for a fix and the LAST thing I wanted to do was erase everything... but it worked for me.
I saw white icons and faster knock-on response. That was all, other than tap to pay for my Google Wallet. I know it isn't all performance and that some of it is security and under the hood type stuff though.