Bristle nose plecos are good but they only get 4 inches. You could maybe do blue phantom or green phantom but they are very messy eaters and you need a good filtration system.
I wouldn't add to the tank for this reason. The whole "clean up crew" thing just doesn't work. You just end up with another mouth to feed and more waste to clean up. Besides if your Oscars are spitting their food out they are probably being fed too much. If the Oscars are spitting the food out, then you get a net and clean up after they are done eating. You can't rely on a fish to take care of other fish lol.
i think he means all the food flying out their gills but you are right, another fish will probably raise the bioload but at least the food wont be wasted!-) fourlines make great oscar tankmates... a peacock eel would be pretty cool too if you can find a larger one!-)
If Oscars are wasting food, spewing out the gills etc. then feed less or switch to a smaller pellet. Their mouths are bigger than their throats. Even my biggest O's at 12 and more ins get medium sized pellets. They can swallow them whole, no waste. Clean up crew is not suited to Oscar tank, they still produce their own waste, add to the bio load and take up space. Oscar doesnt like a busy tank