Which usually grows faster, burms or retics? Approximately how long would it take either of them to outgrow a 4longx2tallx2deep?

I have experience with boas and I'd like a larger snake but I won't have room for anything larger than maybe a 6x2x2 for about 2 years until I move in with my boyfriend but I know I have room for a 4x2x2. I'm interested in one but of course if they'll outgrow it within that time I'll just wait and just get a boa perhaps until I have the space.