I'd go with the SPD mtb. pedals and shoes. You won't unclip accidentally and you can walk all day in the shoes without chewing up the cleat. Can't do that with road shoes, particularly not Speedplays. If you do a search for Speedplays on the Roadie forum, so many threads will pop up it's like their version of the Kilo TT.

Lance probably wasn't clipped in to begin with at the start of the 2005 Prologue for the TdF. His foot was loose coming down the starting ramp. He did lose that race but only by two seconds to Zabriskie. Sheryl Crow was there and waved at Lance. Then she worried that she'd distracted him and that's why his foot was loose. He said it wasn't that big a deal and went on to win his seventh TdF.

Whatever you get, make sure the shoes fit you correctly. And take the time to get the cleats adjusted just right. Even tiny changes can make noticeable differences in the way the shoe feels. Also the cleat release tension is important. You want it tight but not so tight you can't unclip and are lying in the trail stuck to a bike watching the vultures circling overhead.