In reply to Alexs403:
It can be a pain to find a good fit so I would add that a well-fitting B3 boot needs to do three things:
1) Not have pressure points with thick socks. This can be tried at home, just wear them for a day or so while doing chores and you'll notice soon enough without doing damage to the sole so you can still return them if necessary.
2) Not have toe-bang while front pointing, ie it has to have ample room around the toes. Test this by kicking a wall multiple times throughout the day mentioned in 1.
3) Not have heel lift while front pointing. You can test this by standing on a ledge with the front and doing a bunch of calf raises.
The hard part is that it is almost impossible to get this 100% perfect so it is often a compromise between these three, and it is very difficult to know wether you're getting it right the first time. I went through two pairs of B3 boots before I got it right with the Cubes. Luckily I didn't buy them new