Depends on what AND where I am flying. If I am flying a twin or at a controlled airport I turn crosswind when either directed or 300' below TPA which ever comes first. At an uncontrolled field in a single engine I turn at a visually safe altitude but never lower than 400' AGL. Reason being that if I were to lose an engine at some point on the crosswind I am already going back towards the airport and it would require less of a turn to go back to the runway. Basic rule of thumb is to never attempt a turn back the runway if you lose an engine on upwind due to it requiring more than 180 degrees of turn (see stall spin) However on a crosswind leg there is less of a turn required to get back, that being said though it would still take thorough planning and excellent airmanship to return. I hope this was the kind of reasoning that you were looking for.