For those conditions, softshell pants are the way to go with long johns of various warmth underneath. These are what my wife and I use. We haven’t tried dozens of models in each category, but enough to know what works well for us.
Mild Cool Conditions:
-Patagonia Tribune Pants – stretchy wind-resistant hiking pants great for everything but very hot weather (the spandex content and wind resistance can make them too warm in very hot weather). About 11-12 oz.
-Patagonia Thin Powerstretch Pants with high nylon content (forget model name) – about same weight as Tribune Pants, but a bit more more wind resistant)
Note light nylon wind pants like Patagonia Houdini Pants can add some breathable warmth and added wind resistance to the above when needed for only 3 oz.
40-60F: Cooler Conditions all these work well:
-Patagonia Tribune Pants + lightweight merino or synthetic long johns or midweight merino or synthetic long johns (Capilene 2)
-Patagonia Thin Powerstretch Pants with high nylon content (forget model name)
-Ibex Guide Pants – about 16 oz. each, highly breathable and stretchy with enough wind resistance, though in wet conditions can soak up too much water, with nylon on outside and merino/synthetic mix against the skin
20-40F:
-Arcteryx Gamma MX Pants – highly wind resistant and durable water-resistant nylon face and soft, thin fuzzy warm layer against the skin. Favorite relatively lightweight pants for cold weather. I think they weigh about 19 oz.
-Ibex Guide Pants with long johns underneath
-Craft Storm Tights – windproof front and breathable back with great stretch. Great for cross-country skiing and cold winter running and snowshoeing when you are really moving.
-For cold mixed conditions and mountaineering where there can be a lot of wet from rain or melting snow/ice, waterproof but breathable stretch softshell pants can work well, such as the Mammut Castor Pant.
Below 20F:
-All of the above from 20-40F with long johns underneath. The warmest long johns I have are fuzzy thick powerstretch.
For very cold snowshoeing we use Forty Below TR Light Energy Overboots, which add significant warmth. In general keeping your lower legs warm up to your knees adds a lot of warmth and comfort.
For standing around during rest breaks, I find throwing on a warm insulated jacket sufficient. For in camp, if you plan to spend a lot of time hanging out outside, you can wear down or synthetic puffy insulated pants over your pants, or leave those home and just get in your sleeping bag/quilt and you’re good.