When I was 12, I wanted a Jardini, a clown knife and a bichir more than anything. The guy at the lfs would not sell any of these 3 fish to me because all i had was a 55. I hated him. I earned the money for those fish (a lot of work), and I still could not get them. Later, I have kept many other fish and have somewhat matured.
An 8 foot from a 4 foot changes quite a lot I think.
Yes, I wish I could keep my 14 Praecox in a 8', they'd be much happier than in my 55(yes, the same one.)
Anyway, I have kept 4" gouramiis (don't know what kind, its a long time ago, no pics) in a 10 g and a 55g, with no difference in behavior. Each one picks a plant and guards it. End of story. However, I am sure my <2" juvenile Praecox would love a bigger tank, especially a round one. Their 4' 55g is not really big enough, as soon as they start to swim, they have to turn around.
I feel it goes by the fish. If it is behaving the way it should in your tank, it is big enough. Anyone who has an understocked tank is wasting its potential. yeah, I want my fish to be happy, but I keep them for me, not them. In aquaponics, the stocking density can reach 5lb/gal with healthy, spawning fish. Yeah, they have awesome filtration - you can get the same. No, I would never keep a display tank like that, but I am planning an aquaponic system, and yes I intend to go with incredibly high stocking density. As long as the fish can swim naturally and are not territorial or aggressive, they may actually like the security excessive numbers of tankmates give them. Look at any shoaling/schooling fish in the wild. A whole river to swim in and they cluster together, bodies almost touching.