They are quirky, that's for sure, and, thus, fun to observe.
Mine 5 are about 10", 5-7 years old, three standard-looking blochii, one with crisp dots as opposed to the common muddled pattern, and one, the smallest, with clear 4-lines, I think this one would be most correctly called a 4-line Pim, Pimelodus tetramerus, which indeed maxes out at smaller size versus blochii.
The one with the crisp dotting was sold to me on aquabid as Pimelodus maculatus, which it is not, of course, because it has the black mark by the dorsal front base, the signature of the blochii type Pimelodus.
They school together ~75% of the time. Their interaction with tank mates is fun too due to their inquisitive, spunky, highly energetic nature. They are really fast, can be crabby but most usually just curious and explorative.
When they are healthy and hungry and stress-free, they feed in a wild frenzy, sometimes irritating their tank mates to no end, as happened with my e-cat who would zap only them out of 50 others.