When bananas are rootbound, they continue to grow leaves but don't really get any taller, and as mentioned the corms will start to push out of the containers eventually. However, if you plan on planting them in the ground eventually (doesn't have to be anytime soon), being rootbound doesn't really matter. If you plan on storing them, keeping them rootbound is actually a good idea in my opinion because they will not die if they have good care and they will stay small and easy to handle. You can't really overpot a banana because its roots want to spread out so much (with bananas, area is much more important than depth), so no matter what size container you put it in, it will become rootbound.
Also, you may want to increase your planting depth, even if you aren't growing for fruit, planting them that close will eventually end up as lots of competition and probably will not look as nice. Since bananas form mats, planting them even 8-10ft apart will eventually make a dense stand. If you want it super dense and impossible to penetrate, I wouldn't go closer than 5ft, but whatever makes you happy
