For calves: not so much a problem. For heels? Very serious heat flow because the pressure is enough to reduce insulative value of down, or to move it aside; and out of the feet flows the heat.
I hope to settle on two layers of stiff-enough wool socks. (I've got one fairly dense fairly fluffy set for this purpose.) They breath, don't compress -- that's the "stiff enough" part--they insulate, and they wick away moisture.
I agree on the pad-shift. I've spent too much time trimming, and tailoring a cheap blue foam pad which still shifts within the footbox. From reports elsewhere, evazote would be better. Should you think of going to a top quilt, go to leiglounderquilts.com for Hangnout's video of his system of integrating the pad securely in the TQ.
The point of this discussion that is Clark-specific: Who needs or wants the bulk of that large triangular pad that is part of the Z-line system?