Ive worn their gunflint 400g for years, as long as I am moving/standing ive never gotten cold feet. Usually the opposite, hot and sweaty. The pair i bought last year tore at a stitched seam this summer and their customer service is awesome! They couldn't locate a replacement pair anywhere so they gave me a coupon for a free pair of boots (any boots).
I was going to get elk tracker but ultimately settled on the vaprtrek in 8", they are so lightweight its like wearing tennis shoes. Im not sure how the uninsulated will be for late season upland, but so far dove hunting and working the dog this fall they are great. A good pair of socks is more important than insulated boots IMO.