I looked up the Hydor Koralia Nano Evolution 425 gph and I was already impressed with the performance in the video. Seems like a really cool circulation pump (powerhead, but not like your father's powerhead).
It would turn over a 55 gallon 7.728 times an hour, if that helps at all. Petco says Hydor Koralia Nano Water Circulation Pump is for 28-50 freshwater gallons. I think that is the older model that yours replaces. Your model takes less watts of power, so it doesn't heat up the water as much - probably not a major issue.
Doesn't have a speed control, which should not be a problem in a 55 gallon. Might be able to use a lamp dimmer or a Hydor controller for that.
I have been thinking about positioning my new filter in terms of the filter output direction and how it affects the total tank circulation. I guess you may, too. I think that, ignoring the fluidics issues which I don't know, like what happens when a stream of water hits the glass, I come up with your basic pool ball physics.
Also, I'm not going to pay any attention to creating surface agitation - the filter will create sub-surface movement of the water, which is what I think you'll be doing. So hopefully, CO2 retention in the water will be maximized (my tank is low tech) while surface area and gas exchange will be minimized
MY TANK: Planted 10g; 2 x 10W CFL; Fluval U2 internal filter; MGOCPM/black sand cap
A Silent Cycled Tank