You're bio says you have a 50 gallon tank. I had a 55 and some folks said it would be OK to put in a kole tang since I was planning to upgrade. Koles are in the family of bristle tooths that can be kept in the smallest tanks. I decided to be patient and I am so glad I did. He is still only 3" long (boy they do grow fast), and he covers every inch of my 120. All day long he cruises and inspects and polices and eats algae. I built in a lot of caves and tunnels to give the fish stimulating swimming routes instead of just circling the tank, and he is all over it.
I think if I had put him in the 55 I might have thought it was good enough lacking anything to compare it to, but I would have felt very guilty once I saw him in the 120, cause it's not good enough.
Further, I would have had to dismantle my rock work to catch him, they are fast and can really snug into tight spaces like you wouldn't believe. So once You have the whole existential crisis of deciding to give up a pet you've gotten attached to (they are friendly fish) because it's become unkeepable, you have to attack it with a net like a mean jerk.
And that's just a kole tang. If you're thinking of something more ambitious, you're dealing with ich risk and aggression and all sorts of things.
How would you even know when it's time to move?
How would you move?
Where would you move it to? - do you have a friend with a big tank who has already committed to taking your leftover old busted up fish? Cause selling it back to an lfs so they can sell it to someone with a 40b isn't good enough.