I have been running CandyKat + Insanity for a few days now with stock brightness settings (which is actually really bright). Along with Greenify.
I still get good battery life. Probably around 3-4 hours screen on, and all day use. To my surprise, I do seem to get long run times with video - I tested 5 percent per half hour. So if it continues - 10 percent per hour. That's a long time - that means the phone can play movies for 9+ hours. I was using the Snap movie viewer.