Anecdotal evidence, but I went and bought a pair of stiffer soled shoes and some Look pedals to replace my Shimano road/touring spd. Wore them on a very hilly 200 (4.5AAA) and felt the difference with the power transfer immediately and did not get hotfoot. It was a very warm day. I feel sure I would have been struggling after 100k or so with the old set up. Prior to this, hotfoot was the limiting factor on my rides. One swallow doesn't make a spring, but this is a very good sign.