I'm in Vancouver and went into the Australian Boot company to try different styles on today.
I did not buy anything but came away with some helpful info.
I wear the 4.5 in the women's heeled boot. It fits well and I don't need an additional insole because the tilt of the last and the extra rubber on the heel means I don't get PF from it.
But I want a flatter boot for my walk/hikes.
I learned that I need a size 5 in the round toed or classic boot (women's or regular) but that in order to make it fit even remotely, I need TWO insoles -- the regular Blundstone insole and my superfeet green insoles.
Half sizes, as someone already said here, do not affect the length in Blundstones, only the width-depth. But you don't need a "high volume" or wide foot to benefit from a half size -- it also works better for anyone with a higher instep (that's me.)
I wear a 4.5 in the chisel toe and can fit my Superfeet insole into it.
The chisel toe would probably be my best bet for a flat Blundstone -- but the problem is that the treads on that boot are not as grippy. So I'm still in a state of indecision but at least now I know what size I need in which style and how to make them fit me properly.