I use TWRP 18.104.22.168, AOKP KitKat 4.4.4 6-28-2014 ROM and KT747 7-3-2014 Kernel. I decided to use ART instead of Dalvik. In TWRP Recovery Menu, there is no option to wipe ART cache, only Dalvik. It may sound dumb to ask, but does "Wipe Dalvik Cache" option works on ART cache? I thought maybe both of them use the same folder, so cleaning Dalvik would clean ART, but I am not sure anymore. I do know that even if you use ART and then perform a Dalvik cache wipe with TWRP 22.214.171.124, your apps will have to go through the long re-caching process after a reboot. This does suggest that cleaning Dalvik also cleans ART, but again - I don't know and need to be sure.