The effectiveness of bio media is greatly reduced if it's caked with waste, as is the case where a canister filter is doing a lot of mechanical filtration and isn't frequently cleaned (and/or has a frequently cleaned mechanical pre-filter).
Peacocks, haps and most other Malawi cichlids are tough fish and will do just fine in just about anything but liquid feces. Believe me that there are no shortage of African cichlid tanks being pumped through closed canisters of waste that only receive a bi-annual rinse when they finally gum to a trickle.
My advice is to not overthink it: A couple of any decent HOB or canister filter(or better a sump) will more than handle your tank, especially if you're doing regular (weekly or so) large water changes. And clean your filters regularly.
Spend as little or as much as you'd like. Research to your heart's content. Argue about whether one shape of plastic thingy is superior to another. In the end, you could drop a couple of airstones in a sponge filter or three (or behind a piece of Poret foam)...add a box filter for mechanical filtration...and it will be all the same.
Matt
The capacity and efficiency of mechanical filtration is controlled by the flow through surface area. Once a thin surface layer of the media is clogged, the flow is restricted and the rest of the media volume does not provide more mechanical filtration, only biological. The media volume of a canister is much larger than any HOB, but media area is not that much larger. So if the canister flow does not slow down for many months, by pass is occurring.
