The surface area of the tank is where gas exchange occurs and has little to do with the filtration method.
Increasing surface agitation will in turn increase gas exchange, this is because the surface area increases with the folds of water, it makes the water surface greater.
(It was explained to me like this) take a 2 foot square piece of foil, keep it flat, that's the amount of gas exchange available with still water, now take a 4 foot square piece and crumple it so it fits within the 2 foot boundary, now you have all that extra gas exchange with an agitated surface. This can be achieved with power heads alone and they have very little actual filtering ability.
The filters have several stages within them, mechanical, biological and sometimes chemical. The end results are usually quite similar.
Nitrate. This is what water changes are for, nitrate reduction.
(Although this is simplified water changes do a great deal more)
The mechanical filter element will remove suspended matter, decaying plants, fish waste (solids) and that type of thing, this is usually sponges followed by a floss, the floss element takes care of the finer particulates.
Next up is the biological stage, these are normally ceramics or sintered glass, this area is where the ammonia and nitrite is converted into nitrate.
The chemical element when used is wide ranging, many things can be employed here to perform a similarly wide variety of tasks from phosphate or nitrate reduction down to tannin removal depending on what media is used.
You should rate your filter to the type of fish you are keeping, a high turnover would not suit slow water fishes (bubble nesters etc)
A slow turnover is not ideal for fast river fish.
Another thing to take into account is the mess the fish makes when eating, messy eaters normally have a more powerful filter system fitted.
The amount of water you need to change will depend entirely on the stock you have and the amount you need to feed that stock.
The amount of mechanical filtration you need will depend on how much mess the fish make. Big sucker mouth cats will easily need double that of regular fish.
Having said all that, there is nothing that replaces a water change.
Hope his helps.