I did not unroot prior to updating. The 4.3 update was installed via kies on pc. Had a lot of issues after the update similar to all those reported (fast battery drain, lag, inconsistent wifi performance, etc). I did not do a factory reset because I was lazy and didn't want to setup everything all over again. Though in hind sight it would have been the best way to go to avoid all the problems.
Here is what I did to get root and get rid of the problems.
- clear cache partition
- root using Cf auto root & odin
- install SuperSU via play store. It will complain that binaries are not installed & reroot is needed
- reboot & reroot using cf auto root
- run supersu and it will now install the binaries and you'll have root access
- reboot & select the Cleanup reinstall SuperSU from play store option (may not be necessary but seems to clear up some weird issues for me), reboot
- install Titanium backup and view your apps filtered for 'knox'. Freeze/disable all 6 or so entries. You're now knox disabled
- install Goomanager & run the Install open Recover script option which you can use to install twrp or cwm if you want a custom recovery
- boot to recovery and use to clear cache and dalvik cache, followed by backup