My opinion is always going to be bigger the better. Or improvising and doing a 4x2 with a 2x2 attached to it - boaphile makes solid walled pieces that you could use as a hide/nesting site.
I will be doing 6x2x2 for everyone once they get to size, but I want to make sure they don't need bigger.
Also, if you do bare minimums, I feel the snake should be allowed to stretch a little more often outside of the enclosure.