Oh what I'm trying to say is you are using 3G for data but cmykay is using WiFi. Big difference in power consumption there.
I do not have a WP8 phone. But from my experience with WP7.5, there are a few things to consider to save battery life:
1) Turn off screen brightness sensor by avoiding Auto mode (I think you had done this)
2) Minimize Live tiles usage. Those animation and network-dependent status updates consume some power. The more you use it, the more it consumes.
In fact for apps that you do not need to use frequently, it's advisable not to create a shortcut tile.
3) Location (GPS?) switched off if you do not use it.
4) Try to use Edge if you are not browsing/idle. I think this alone saves a lot of battery.