I come on these sites a lot and offer little advice and I was recently called out on it by a good friend. First off congratulations on the hunt!
I am a cameraman and filmed over 2 dozen sheep hunts in North America Both rifle and bow. I get this question all the time. There is no perfect boot and an August AK sheep hunt is much different than a December Ak hunt etc... I've read through the thread and is a lot of good advice being given here. Some added 2 cents:
1. ask your guide or other guides in the area you'll be hunting and listen to what they say! Don't get caught in marketing traps.
2. try them on and break them in! Sheep hunting is awesome but a mental and physical challenge, more sheep hunts have been tipped toward the negative with bloody feet!
3. Train your feet. Here in Arizona I will walk barefoot once or twice a week in a wash or on sand to condition my feet. Haven't had a blister in years and I go in heavy with all my camera gear!
I love the folks at Kenetrek and Lowa was giving me boots for a while but they are heavy. If you aren't accustomed to wearing heavy boots i would consider the Crispi or other lighter ones. Anyway I don't mean to ramble on. I could talk about this for hours.