I've taken a complete set of Buffalo gear through hell and high water. (High water meaning completely submersed in a lake, by the way!) When worn next to the skin, water just drains away, even after total immersion in the depths of winter, and no matter what disasters befall you, you'll feel fine. I was told by the manufacturers just to keep on walking, and on no account strip off the gear, wring it out, or hang it to dry. It's tough stuff and it works in nasty conditions, but you wouldn't want to be sat next to a roaring fire in a pub while wearing it!
Having said all that, if you're careful about your choice of base layer, then I don't see how you'll come to any harm. A thin wickable base layer will do fine, and you won't have the Buffalo itself next to your skin. I once met a guy in Belfast who was wearing a Buffalo shirt with a cotton teeshirt underneath, and he complained he was always getting cold and wet. I mean... cotton teeshirt... what does the guy expect?