Keep in mind that bigger is not always better when it comes to BP cages.
In the wild, they spend most of the day in a termite mound hiding. At night, they come out to ambush their prey from the entrance of the termite mound. Then they go back into the mound to do it all over again the next day. To put it mildly - they don't get out much and have earned the nickname "Pet Rocks of the Snake World" for a reason.
In addition to the above, it is important to think about how easy maintenance/husbandry is going to be for the both of you with a larger cage. More space = more to clean = more to regulate properly.
Don't get me wrong - I'm the last person to call into question an order from Ali and Animal Plastics, but just keep in mind what's best for Oliver when you ultimately make your decision.