I used to wear the Danner boots with 400 grams of insulation for duty. They were pretty warm even in the snow but I was not sitting or standing still in the snow a lot. Have you considered a pac style boot? They have some thick inserts and you can bump up on the insert thickness if the one you have isn't enough. I tried a pair of pac boots for a cold weather blind hunt last winter and they were very comfortable. I hiked less than a 1/4 mile to get to the blind and the boots were reasonably comfortable for hiking that distance.