I am using 2 x GE9325 55 watts in a fixture made from the 2 x 55 watt bright kit sold by www.ahsupply.com
The fixture is suspended over the 20 US gallons high aquarium and makes for a high light situation requiring a good deal of maintenance. You could use the same sort of system but have one 55 watt GE9325 instead. I should think that would work well too.
I've been using the 1 x 55w bright kit to which Andrew referred for several years, and I have not had difficulty growing any plants (as long as other factors such as CO2 and fertilizers are addressed). I have had success with a variety of foreground plants such as glosso, HC, various hair grasses, riccia, etc.
The only drawback to using a single PC bulb over a 20 high is that it doesn't provide even lighting from front to back. By bending the reflector that comes with the 1 x 55 kit in a manner that "opens" it a bit, better spread of light is achieved. The only time I have noticed it being an issue is when plants are grown very tall in the back. The upper fourth of the plants in the back appear to be shaded. With that said, I prefer the ease of maintenance that 2.5wpg affords compared to doubling that with a second 55w bulb.
My dual AHS reflector is quite wide and allows light to be blasted on the front and back glass of the aquarium. Unless the water chemistry is well adjusted, that can lead to a lot of glass algae. In order to use two 55 watt bulbs, you have to cut one of the facets off each AHS reflector and then join them side-by-side. Alternatively, you can buy an 'expandable' [______] shaped reflector. That might also help limit the light hitting front and back glass panels.
I have the two lights about 10 inches above the water surface.