As they say around here, 'I don't have a dog in this fight' but I will say that if a person wants to ride clipless and wants to increase efficiency a local guy might have the answer.

He does group rides with one foot clipped in for about half the ride (10-12 miles) and then uses the other foot for the rest of the ride. He also appears to have about 1% body fat and looks like the cover of an anatomy text.

As for me, my knees are sooooo bad that I'm afraid to even try clipless. If I fell, and was clipped in, it would possibly mean a TKR (Total Knee Replacement).