Your first post was almost written by me... except I switched from Speedplay X-2's to Dura Ace which I think is similar to the Ultegra pedal. I still get hot spots but not as bad. The Dura Ace pedal like the Look pedal has a broad platform.

I've tried it all - carbon soles shoes, different shoes (but I always come back to Sidi's), socks, fittings etc, I still get hot spots. Doctor has explained my foot has been injuried over and over again and I have a neuroma and I just have to deal with it (or have surgery). The wider platform helped a lot. Having good fitting shoes (not to wide or too narrow) shoes do as well. But I just know my feet will start hurting (around 40 - 50 miles) and I have to 1) wiggle my toes around, 2) stop and rest my foot, 3) unclipped from the other pedal (alternating my feet), 4) spin not push etc.

As to socks, most cycling socks are pretty thin which is why I like them. I like Defeet, SockGuy, Pearl, etc. Most are thin, supportive and comfortable and will wick away moisture (also important).