Sorry you are having problems, but thx for this post. Nothing like the composite of great minds together. I have some blab of my own going on about what SpeedPlays to buy partially due to a similiar issue with my feet. You just aided in making my decision.
I am using a double sided mtb pedal that came on my road bike. SPD Shimano M505. Small surface area. First I rode in my mtb shoes that I wore to spin class. Diadoras. Not so stiff sole, major foot numb issues, etc. Then, I upgraded to a true road shoe. Sidi Zeta. Things improved with a stiffer sole, but I still don't think it's stiff enough. Next will be the all carbon. I wore the mtb shoes with that bike this w/e and both feet were numb. They are pretty flexy, that confirms the sole theory to me. Sigh...
Don't you just wish there was a Cycling Santa Claus that came in July and drop a bag full of bike goodies off at your front door? I'd put up a pine tree decorated with bike chain as garland if he'd come visit

. But, I digress with my fantasies

... back to feet...
Socks... I get the bunched up sock issues. A tri friend of mine does just as posted. No socks. I think she's onto something. Here's my sock tries... mainly Pearl Izumi's. The x-static (men's race sock) and originals are pretty much the same thickness. The x-static bunches a bit less. I tried SheBeest no show socks, sorta thin, but bunch too. The PI Kerin sock is very thin with a arch center support... still bunches some in the toe for me. PI ladies ankle attack sock.... thicker than Kerins, but nice stretch forming factor, no bunch as of yet. PI also makes a silk lite sock which looks really thin, but in the pic on the web it looks baggy on the model's toes... wonder if it would bunch up like the Kerin? ...sooo, didn't try that yet. I have tried smaller socks too, but the heel placement doesn't fit right then (thinking they would bunch less in the toes). Any bunches equals foot pain.
I have not seen the SpeedPlays first hand, but been doing a lot of reading on their web site... think the X pedal is the widest contact for what they make in roads??? Would your lbs let you trade em in for a try? Could you sell your current SpeedPlays if the other worked to offset the cost? Maybe SpeedPlay customer service direct could help if you have not called already.
Just some more ideas, fwiw.