you will probably get a lot of mixed opinions on this subject but heres my 2 pence worth
mine has lived in his 3ft viv since he was small enough to fit in my hand, we did have some feeding issues at the start but now hes fine and iv had him over a year.
but yeah you are right it will depend on the snake. if the snake is very young it wont do him any harm living in a RUB and then as he grows up he can move into bigger rubs or maybe go into a viv that he can sty in perminatly.
its a bit of a gamble, id say if your goin to be getting a young snake start with a rub about 30ltrs or so god knows what that is in gallons sorry lol but then work your way up from there. saves you money as well!
some one will be a long with a shorter more helpful reply soon dont worry lol
best of luck