I have been using my Lowa GTX mountain boots for stalking and outdoors in the most extreme weather for 7+ years, and i was advised when purchasing to go up
at least half a size, but a lot, of course will depend on the type and thickness of socks that you wear with them.
As for the boots themselves, i am very satisfied, they have served me well and kept my feet warm and dry.
They are a firm boot from new, and seem to stay that way, but with no discomfort, and little or no wearing in period.
The only downside i can report, is that the soles (Vibram i think) can tend to be a bit slippy and unsafe on mossy and/or wet rock and care
must be taken, as i know to my cost, when transporting a £2.5K stalking rifle and optics