It really depends on what you want from the animals you keep. Me, I like to interact with them. I love snakes that are watching me back & fun to hold.
I used to keep & breed bull & gopher snakes: they are active & need a good-sized cage...they're diurnal too. Adult size is about 6', very slow growth after
that, & 7-8' would be exceptional for sure. All snakes grow their whole life, but it slows way down. For me, 6' is a nice size, & though it seems huge when
you're new & thinking about a future snake, they grow slowly. Also, a 6' rat or bull snake is MUCH lighter than a 6' boa. Rat snakes have a more slender
build than a bull snake, but either one is nothing like a 6' boa. BTW, there are also some smaller versions of gopher snakes, about 4' I think...I never dealt
with them though.