There is a S. brasiliensis with almost that size in a LFS near my home! When I go there I will take a picture! He is with a 3-4 ft arapaima gigas and some HUGE peacock bass!!!
18-24". If you look at pics of ones caught in the wild, smaller fish tend to be more silver just like in the aquarium. There is also quite a bit of variation in large specimens in the wild, too. I suspect that gender, water conditions and season will affect color of wild ones. I've noticed that most, though not all, of the best colored ones seem to be males from black water.
