I have been experimenting with 3 keywords of the the past month and a half. I tried 1 keyword, got the $ average. switched it after a few weeks got the $ average and so on.
This took much longer than 1 month and a half to decide on which keywords work best,..but ive increased my click average about $1.40. Giving me an average click now about $1.71
Im working on a keyword popularity formula.
Ill keep you posted.