Some days further, and some experience more. First to start with 720p recording doesn't work on pwck. I can't use the highest resolution, it gave black viewfinder + recorded video. I powercycled my phone twice to eliminate other bugs, but it didn't help. Also I noticed stuttering in animations while on pwck3, except from the animations it's really smooth. Then I installed power-kernel from extras-testing again, and after 1 power cycle, all video resolutions worked and the animations were smooth too. Maybe these issues have the same root as both have something to do with visualization. (Maybe useful to remark: use HW_Sync = 1) Still I think pwck is smoother when I/O / cpuload is higher. No evidence, just my mind could be wrong though as I also played with swapon and swapoff. Also the difference isn't big, I am now on kp49 and only had 1 situation while the UI was lagging while on pwck I had none, if I remember correctly. Except that the animation/transitions were stuttering.