Charlie, a few comments; that test really helps isolate your issue. IMHO you need some combination of the following: insulated soles and/or the ability to pull up on the pedal stroke. If you are constantly pushing down on the pedal you squish out all the insulating air and will suffer heat transfer even with plastic pedals, maybe something like Power Grips might be to your liking. My first year or two on the bike I used winter hiking boots which worked well for the distances I was doing then.