I don't really think there's a general answer to questions like this. Those ArcTeryx of yours are pretty specialized pants and I can't imagine wearing them in the summer or for lying around the house. And you'd also likely want a pant shell with them for extreme weather use.

That being said, my winter gear is most definitely separate from my summer gear. I have technical Marmot mountaineering pants which have a separate 3-layer Goretex shell, and I've worn them everywhere from snowmobiling in New Hampshire to Antarctica. It's the best cold weather gear I have, but you couldn't pay me to wear them in the summer -- not because they'd be too warm (they have no insulation) but because they'd be too bulky cause they allow for all the other layers you'd wear with them to stay warm.

Summer time is BDUs with nice light 2-layer Goretex on top in the rain. Very cool and comfortable. The BDUs alone in bad weather suck because they absorb water like a sponge and take a while to dry. If you keep them dry in the first place, you don't need to worry about it.

Finally, I think good underwear may be a more important consideration. <img src="/images/graemlins/smile.gif" alt="" /> The CoolMax brand is totally amazing and if you're really active outdoors, I don't know anything better for keeping your body comfortable.