I'm really not much of one for insulated boots, but if I were buying a pair I'd probably not go over 600 grams. Most boots I wear are uninsulated, and with a sock liner under a good pair of wool socks (Smartwool), I can go well below freezing before comfort starts to suffer. Whatever you decide, do not overlook the importance of the socks and liner, as that can make all the difference IME.