My galaxy Nexus is no longer supported by Google (BOOOO!) but I have been running CM11 (4.4 KitKat rom) on it. It's been really awesome. I also have experiemented with running ART rather then Dalvik, and have found ART does seem to improve battery life and reduce the freezing, lag, stutter, and random reboots I was experiencing on 4.3 (both factory stock and custom roms).
Try it out. The only downside is not all apps are coded to support ART so some may not work properly (or just simply not work at all - although I haven't run into that!) For me there have only been a few apps that don't play nicely with it (And it could be that I'm running a custom ROM - and nightlies at that!), or that I'm running ART (which CM specifically states that it is not officially supported by them)
Make a backup, switch to ART and see if you like it. Be aware that you will be asked to reboot your phone so the phone can recompile the apps in the new runtime. You only need to do this when switching from ART to Dalvik or Dalvik to ART. The switch to ART takes significantly longer for the initial boot and recompile but after that reboots seem to take about the same time.