Cool, can I ask why you have like twice the amount of filtration on your tank?
What wavemaker would you recommend?
I can't speak for steveo, but there are several reasons to use a larger filter on a tank.
First off, manufacturers tend to be "very optimistic" about how large a tank the filter will support.
A larger filter will often have larger or multiple filter pads, so less time between filter cleaning.
You'll get more flow out of a larger filter, so you may not need an additional powerhead.
If your talking about a true wave maker it's tough to beat the EcoTech Marine VorTech Propeller Pumps, but they are out of sight expensive, and massive over kill in a 20 gal tank.
On my 90 gal planted tank I use the JBJ Oceanstream Circulation Pump/Powerhead and Duo Wavemaker Kit 500 gph. Still over kill for a 20, but a reasonable price.
For your tank I'd sget something like the Hydor Pico circulation pump, or any other decent pump