I'm using two-bolt SPD cleats (eggbeaters on both bikes) that are adjusted to be under the ball of my foot. MTB shoes, laced. Numbness (and pain) starts at the pressure point under the ball of my foot, right over the pedal axle.
I'll definitely try loosening my shoes! I've always liked them to be cinched up, so that seems to be an obvious change. Next chance to ride is tomorrow, so I'll try it then.
It was funny after I changed the pedals back, I noticed that my foot was lifting off during the upstroke. I must use the clips more than I thought. I'm thinking about going to a two-sided pedal for my MTB, I ride just enough places where I want the ability to quickly dab a foot without having to unclip.