I'm not convinced that road type pedals (i.e. bigger platforms) vs. spd style are more efficient. All of the power is being transferred from the foot to the cleat to the pedao to the spindle regardless.

The hotspot phenonmenon has little to do with the cleat and more to do with the shoes footbed and your own foot and the nerves in it (trust me, I know a little about foot anatomy). If you experienced the hotspot phenomenon and switched the cleat type you changed multiple variables - only one of which was the cleat type.

Anyway. I run single sided SPD's with cheap shimano lace-up SPD compatible shoes. All I can say is get shoes with VELCRO or similar straps - my laces have gotten caught a few times and they often come out of the shoe when I stuff the loops in there. It's also hard to tighten and loosen the shoe while on the bike if you've got laces.