As others have said it depends on how cold it is out and how active you are,walking versus sitting.Keeping your feet warm is more than what boots you have on it is keeping your hands,head and core warm.If the rest of your body is plenty warm your feet wont get cold as easily.
If you are on stand for extended periods of time I would buy Ice Breaker over boots and put them on once you can situated on stand,warm dry socks,loosely fitting 600 gram boots,and the Ice Breaker over boots will keep your feet warm.If it is really,really cold puttign your feet directly in the overboots with the warm merino wool socks and a couple of disposable handwarmers placed in the cinched up over boot will do the trick.