I recently got a size 3 Zoot Sports Men's CompressRx Sock 2009. The sizing for these socks aren't based on foot size. Instead it's based on calf size because the focus of this sock is on calf compression so it makes sense. For those of you that are curious I wear a size 9.5-10 shoe and the size 3 fits fine. Since it's pretty flexible around the foot I can see it fitting a wide variety of foot sizes.
Performance: While I have worn these on short runs and rides these times were not when I noticed the biggest difference in performance. I noticed the biggest difference in performance on a day I was at a trade show walking/standing on my feet from 7am-7pm. Normally my legs would be either sore or fatigued by the end of the day. However, the day I wore these my legs still felt strong by the end of the day. I also tried on the Zoot CompressRx active compression tights for a different day and seemed to have the same results I'll save the details for another review.
You can buy the socks here: Zoot Sports Men's CompressRx Sock at OneTri.com
Note to self: Don't forget to write reviews on the following products, Profile Saddle, 2XU Velocity Wetsuit, Orca RS1 Wetsuit, Zipp wheels, Profile Design Aerodrink V2, Scott Plasma, Aquasphere Kaiman goggles, Zoot CompressRx active compression tights, 2XU Recovery socks black.