After having 4.4 on my Nexus 4 for a couple of days and 2 battery cycles, I tested out how much battery life I could get out of it.
This did include 3G/HSPA+ use out in town (I don't have LTE here), Wifi at home (so very stable connection), lots of web surfing/Chrome use, lots of Google+ and of course playing music via BT in my car.
It looks to me like Android 4.4 KitKat has done some major under the hood tweaking that will help in both speed and battery life of "older" phones. (While I am rooted, this is the stock 4.4 OS and kernel. No modifications done).
I consider this a pretty big improvement, at least on my Nexus 4! This is more than I ever got before on 4.3 by more than an hour of on screen time!