Can you explain what ART is?
ART is android run time. Normally when opening apps e.t.c information is written in the dalvic cache , which uses more processing power and time. As a result things don't run as smooth as they could. ART is now released on 4.4 as an early development option and does away with that . If you Google it you will get more info.
If you run into problems using ART as some have you can flash the moto dalvic patch instead which optimizes dalvic to run just as fast , but I personally think ART has the edge.
Sounds complicated but its no different from flashing a patch through recovery ( for motor patch only) .
ART is found in the developer options on your phone, switch to it and your phone reboots and takes a while as it optimizes your apps.
After you choose one of the above your phone should be as smooth as an iPhone or windows phone.
Just Google and you will get it as there is loads of info on the subject who can explain it better then me.
Hope this helps. J:D