Thats right when you deploy the startup map of the UDK on a 4th gen device that is what you get on performance! When you point your view down it gets even to 23 fps! Its ridiculous if you ask me.
Now it becomes pretty clear there is no chance to get any game run smooth on 4th gen devices with this engine.
I hope there is still a chance that its get improved one day but at the current time its more likely that we will have to release our game only for the high end devices which will be of course make it very unlikely that it will be any commercial succes and it will have no chance to get in the ranks. Past updates of the engine have also shown that there was never a improvement in performance, in fact it only got worse: http://forums.epicgames.com/threads/850320-Performance
Dont get me wrong here, i dont want to talk the engine down, in fact i love to work with this engine, the poor performance and some other shortcomings on mobile just make it very frustrateing. Mabye you like to join here in the demand for a better performance and someone of Epic will finally care about it.