As for the size, minimum requirements is generally 2/3rds of the adult length of the snake and 18" deep. So a big female at 6' would need the 4'. My daughter's snake is older and done growing right at 5', so the 3' long enclosure is plenty for her. She seems happy with it and came from a tub environment, so she does better in the smaller enclosure. My BP isn't quite a yearling, just under 600 grams, and is doing very well in her 2x2 side of the T8. Plenty of room for 2 hides, her water bowl, and a little faux leaf/vine clutter. She's going to be a big one, so I will likely give her the whole T8 once my baby SD/D Retic outgrows the other side of the T8 he's using, lol. I'll be getting him the T10 for a little extra height so I can put in some climb-y things. They're only semi-arboreal, so I don't plan on getting anything taller and the 4x2 space should be plenty for him. The other SD Retic is in a 28 qt tub in a rack right now while she settles in. I'm trying to decide what to get her... She'll be fine in the rack for another few months while I do. I'm not opposed to racks at all, I just prefer my snakes on display. The racks I use for quarantine and during cleaning.