Interesting to me, I ride a triple, but my basic process is to just stay in the middle 39 almost all the time, using the full 9 at the rear. When things get going steeply upwards, I work my way down the small ring until I can't shift anymore, and when I get going downhill, I go up the big ring pedaling slowly until I can't shift anymore. Basically, though, 39/12-27 covers almost all the riding I need to be concerned with.
I weigh over 2 bills, but I don't know how big my guads are. I can take a photo with a $5 bill if it helps, though.