If it's overstocked you would be best served to aim for maximised biological filtration. A pair of cannisters such as Eheim 2215's would give you 5 times turnover and an enormous amount of biological filtration.
Of course it always depends on what you consider a high bioload. I ran a pair of 2217's on a 65 US.Gallon aquarium and can attest that although it kept the water crystal clear it gave the fish what appeared to be an uncomfortable time maintaining their position.