Haven't tried the Sitka or SG pants. However, I have a ton of experience with the Guide and Axis.
Between those two options, I would look at how much snow do you expect to see during the later season hunts? If it's light flurries with just wind and cold weather but you're not dealing with thick snow, the guides will work fine. They're a hair easier to hike in and they do a great job keeping you warm.
Where the Axis shine is for dealing with snow and sleet before it's gets bad enough to pull on rain pants. They're tough as nails and the added waterproof/resistant materials on the seat and knees are great for glassing in snowy conditions where the guides would soak through.
You could make due with either, but if I were packing for a late season CO hunt, I'd be taking my Axis over the guides.