I've got both the Patagonia Guide and Arcteryx Gamma LTs (found each on sale and couldn't resist a deal). Both are great pants, perform well, and are more durable than you'd think from looking at them. The LTs are thinner and stretchier and probably best suited for the warmer end of your 30-50F scale, though if you wear them with long underwear would be good to 30F. They are great alpine rock climbing pants.
The Guides are thicker and warmer, and are particularly good for snow and ice. Some nice features of the Guides, not found on the Arcteryx Gamma LT, are an expandable pants bottom to fit over boots, a reinforcement panel on the inside pants bottom to protect against ski edges and crampon points, and a pair of grommets you can use with cord to tie the pants down under your boots if you find yourself in snow but without gaiters.