This really isnt a numbers question. You should c/r when you feel that you are maximizing your outcome. Though c/r typically has more fold equity involved it also helps to build a pot if you are called. For this reason I personally rarely do it on anything but a semi bluff or a player who doesnt respect them with a strong hand.

Attempting to c/r from a blind when you flop a made hand is also rather effective as it's often the only way you can build a pot on the flop from these positions.

PK