The bioload of SDs compared to other fish of their size is absolutely minimal. I do overfilter my tank by quite some way though (I have an FX5 on a 29, an FX5 on a 55 and another FX5 on a 75). My 75 has an Oscar, a Convict Cichlid and 13 (yes, 13) Silver Dollars. While I have every intention to upgrade to a bigger tank, I am not seeing any complaints from any of the fish about their conditions or available space. My SDs really love the safety in numbers aspect of their tank and they are (if anything) cleanup fish for the Oscar.
Here is a good video which shows the positive affect of me keeping SDs with an Oscar. But I'm absolutely certain also that SDs do not carry the bioload proportionate to their size. And with their size, they are less than an inch wide even when fully grown, mine spend their time eye to eye and all stay in the same area. The Oscar does not seem bothered in the slightest by the amount of space they occupy, and the Convict spends all his time in his hole.
Take a look.
DSC_2923 | Flickr - Photo Sharing!