I agree 100% about the warmth of silk. My silk long underwear is one of my most prized camping items. Feels almost like it is electrically heated. It also makes blue jeans bearable in the cold (but that is for urban use; I'd avoid cotton while cold-weather camping). I may try the synthetic wicking alternative sometime but it will take a lot to get me to switch. The main downside is that I find the abrasion of walking causes little bits of silk fluff to end up around my socks at the end of the day. This seems to affect the long-johns rather than the tops, and does eventually wear the fabric thin over a few years. A relatively worn-out set of silks is currently in my winter car kit.

Steve