I bought the Corrugate Foundry Pant from First Lite with the mindset of eliminating overheating after hoofing up a mountain--and these pants accommodated me quite well. The vertical zippers are a must have to release extra heat (with long johns).
I am 6' and the 35" in length fits just a little long. Other than that, it's just like buying your normal jean size. I wore mine on a hunt here in Idaho with long john's and was quite warm on 25-degree days. But everyone is different. Hopefully this helps.