I've got an i815, but only use it for wifi. Just rooted it and installed TWRP. Tried a few roms, from Omni 5.1.1 experimental, to a few 4.2 variants, they also seemed to slow down after awhile and lag a lot. Now I'm on 4.4.4 r2 Carbon from daniel_hk and it's been solid for days... it's not seeming to have the slow down issues. I just wish there was a way to disable the radios without resorting to airplane mode. I still might abandon, as one of the things I wanted was to do TiVo streaming, but the stock image of 4.0.4 isn't supported.... aaaand flipping to a supported verson of Android (4.1.2+) has issues because the TiVo app does not work on any CM based ROM's. Unfortunately, the only person I saw that tried a stock P68xx ROM on the i815 ended up without touch input on the device.