Where to put the thin insulation: next to body or over shirt?

Vest …. Easier to take on and off when needed ;)

"Will the Cap 4 over top wick the moisture away better than wearing the wool alone?" That is a great question, which i've wondered about also. I don't know the answer, but i lean to thinking that having a well wicking layer over a more absorbent layer, would tend to speed up the process a bit. Unless you're going for odor reduction though, i would put the wool layer over the top of the Cap 4 provided it's not too tight or constricting. That way, it matters less how much moisture the wool soaks up. Because of the unique structure of wool, very curly/kinky, it can still trap some air even while quite wet, however, when it's directly on the skin, it will feel less comfortable than something that's mostly air space (high efficiency grid fleece or fishnet). In any case, when cold and sweat or rain are involved, no better baselayers than the high efficiency grid fleeces or fishnets, as least as far as perceived warmth and comfort. I also agree with Eric, that the vest would be more convenient, and warmer for the weight. I find as long as i keep my core warm enough, it helps to keep the rest of me warm (slightly less so with hands, feet, etc).