These come as close to everything you could want in a back country pant as possible. They block wind, repel water, they're warm, they stretch and they wear like iron. The only drawback to these pants is the price tag. Luckily Patagonia and BackCountry stand behind them and it should be a one time purchase, making them worth the price for a lifetime pant that has this many attributes.
I normally wear a 33 waist and 32 length and went with the medium. They fit well with room to layer underneath.