As a different approach perhaps look beyond your feet.
As your core body temperature decreases your body reduces the amount of blood flow to its extremes, i.e. your hands and feet.
So you could try wrapping up else where to keep your overall body temperature up. Something on your head under your helmet might just be what you need to keep your feet a bit warmer.
Yeah, I thought about the whole connected-up-ness thing. But as my hands (and ears!) get really cold and then warm back up as the ride goes on, I figured my core temperature was ok. I’m certainly a hot, gasping wreck when I get home each night, just with freezing feet. That said, my feet start to get really cold about the same time as my hands warm up, so perhaps I just don’t have enough blood! Good job my brain isn’t using much, for most of the ride…
Tod – Interesting thought about the cleat being an effective heat sink. Hadn’t thought of that.
Rorschach – thanks for the link. I missed that one!
ETA: Don’t know if it’s relevant, but my feet are warmer pushing a high cadence at speed along the flat than when out of the saddle churning up hills, even with the extra wind-chill.