Thanks, I really will have to look more into Sidas. And as you say, research some military forums on the Svarz anatomix lites; I'd be delighted if they happen to suit me because I trust the brand, but won't push it if not.
Yeah, not many brands are made exactly to size, so couldn't be tried properly in boots. In the past some shops kept samples of superfeet trimmed to their nominal sizes to allow trying on, perhaps they did have people trying to fit them in! But either way, I prefer to choose the size that fits my actual foot shape best - the quoted shoe sizes don't seem so important in trim-to-fit models - thats what I meant by trying them. I still can't really tell until well into a walk (or several walks) of course, but at least if they aren't obviously out of kilter to begin with the chances seem better. It is one reason I like boots with flat soles below the footbed; they don't mess up the profile of the chosen insoles and so allow them to work as intended.
I've avoided excessively supportive arches before, either going for medium ones or else softer ones. But reflecting on that other thread I've decided to pay more attention to circumstances; still using routine walks to keep my arch-strength built up, but on longer ones providing more support. I can tell my feet start getting a bit longer than is normal after somewhere between about 15 and 20 miles (or at least my toes can!), so possibly my arches might be getting over-tired by then. They aren't getting any younger!