I want to follow up on this sparge temp issue. Clearly the previous posters who said that tannin extraction is due to pH are correct. But I would argue that it is also a function of temperature. According to a number of brewing experts (Palmer, et al.) one should not sparge with water over 170* specifically to avoid tannin extraction.
Now I am fairly sure that the experienced brewer who monitors the mash pH, can and does (as you have said you do) avoid tannin extraction above that temp. What I am saying is that this practice should probably be left to those experienced brewers who know for sure it will work - but not for the new brewer nor should it be communicated that this is a general rule.
For the average home brewer the extremely small cost associated with the increase in efficiency is basically of no value, but the safety in being sure to avoid tannin extraction would be far more important IMO.
I hesitated in saying the above for a couple of days because I am not what I would call an expert home brewer, and as a consequence usually defer to those with more knowledge and experience... But I think I'm right on this point. However, as always I am open to being corrected.