The ROM with most SOT for me was Marsh CM13: https://forums.oneplus.net/threads/marsh-cm13.405700/
I was getting average 5 hours of SOT (other ROMs was about 3.5 - 4), on the stable 1.9.7 release: https://mega.nz/#!5xNhXQJB!4HwnbLANCmgno9DJJpxIbiB...
I think you have to wipe /system too before you flash ROM.
Here are his instructions:
Next, download and flash the latest official CM12.1 snapshot. Then, without rebooting from recovery, wipe /system and flash my ROM. This process is necessary to...