I can see your point. Rad efficiency is best measured with the delta between ambient and water temp, not CPU core temp though. Too many variables there, like mount, TIM used, pressure applied, flow etc.
You know why idle temps aren't of any importance to me? Because we DCers don't even know a state called "idle". You might wanna have a go at it, too - head over to the distributed computing forums and pick your addiction (I'd favor WCG )

This is called active member acquisition, you know