For what it's worthy,,,
I'm running CM11 (KK4.4.2) and using AnTuTu benchmark (excluding the graphic test since it failed), I got approx. 10% speed increase using ART compared to Dalvik. Remember though, this is a benchmark program. In real life I saw no difference. Big however.... many programs can't run in ART especially the Xposed system so I'm happy to stay in Dalvik mode.
My phone: Sony Xperia Go (ST27i/Lotus) Rooted
stock 4.1.2 CM11 Kitkat 4.4.4 with Xposed installer
Remember - a little knowledge is a dangerous thing. And I'm lethal !!!