ghost from the past--
circa 1992--i do believe i read in a United Airlines pamphlet-we did our training with them in Denver-- 6 degrees nose up for takeoff.
that is what i have used since i really haven't seen much else until this thread.
when i have the time, if it does appear very busy in the way of weather returns, i will run it up and down to get more information.
also, if new to an area, even when it is cavok, it is good to turn it on, so that you will become familiar with the returns that might be from buildings or terrain in the area. waiting for poor vis or extreme weather, before turning it on is too late.