I got lags using ART. It did provide more free ram, but overall performance was worse than with the dalvik runtime.
Have you tried clearing the dalvik cache? It is a seperate option, in the "advanced" menu in cwm. If that doesn't help I recommend a full system wipe, clear cache, clear dalvik cache and then do a clean install.
I do experience lags. Also, suddenly android does not recognize being online via wifi. I surf via browser, but the store and cm updates tell me I have no internet. When I use mobile data everything works.
Are you using the dalvik or art runtime (if you did not specificaly activate art, you run dalvik)?
ART is working. Taking a long time after first boot. Some apps didn't work at first (Opera and Skype), but did after a reinstall. If you google apps that work (or don't work) you get a list. If your app is listed as working, but doesn't, just reinstall it.
I tried to update without formatting the sd card, but I did wipe everything else when I installed the first nightly. It work great, it's just that OTA updates get always stuck on the "finish boot" and later (after reboot) give me an infinite boot loop. Do you think that the sd card really needs to be formatted? Or would it be enough to just use your gapps for OTA updates to work?
I just tried an OTA update from the first release of Dazz's CM11 do the 12/11 nightly, without success. I got to the part where the phone says "Finishing boot" and stays there forever. After a reboot via battery pull it's on bootloop showing the bootanimation. I had to restore it via CWM (always backup!).
Has anyone had success with OTA update? Do I need to install a fresher install manually to be able to do OTA updates?