I don't see big deal with standby performance. Even my one x standby 7 hours drop 1% only with 3g on for whatsapp etc. And the one x is using a Tegra 3 which is much more power hungry compared to XZ and butterfly. XZ and butterfly using same s4 pro anyways so what's so surprising. I don't know why XZ users rave about the standby time if the butterfly is rooted and flashed with proper kernel + uv I'm sure can get even better results.