I don't have much experience with Vision cages, but I would say the size of a 50 gallon tank or rubbermaid (or bigger, of course) would last a lifetime for a bp. That's what I keep my adults in (well, 55 gallon), and they seem comfortable in them. Someone else can probably give you info on Vision cages.
Um....visions are reale expensive and not totally worth the money IMO. I'd suggest something like a precision or a boaphile. Or even better, a rubbermaid tub.
Whatever you decide to go with, the rule of thumb I have heard is 1' of floorspace per foot of snake. For a 4' adult BP, four square feet of cage space. I keep mine in rubbermaids, so the adults don't have quite that much space, but they don't seem too cramped. I get them out to exercise 3-4 times a week.
Randy
"I think it might be helpful for everyone to remember that the purpose of a forum like this is to EXCHANGE IDEAS, not dictate what is right or wrong or good or bad. If you disagree with what someone else is suggesting, you can say so without being argumentative or completely slamming the guy (or girl)." - Smynx