It would be considered very high light. The sticky at the top of the lighting forum has all the info you need.
Watts/gallon isn't applicable here. It works well for T8s and PC lighting, due to the light output vs efficiency they put out. T5HO are much more effecient so they put out more light for the same watts used.
To get watts per gallon you take the watts (24+24) and divide it by the tank volume. So 2.4. It that were PC lighting, you'd have med-high light. You would probably be set with one 24 watt bulb over that tank, and still have more light than you need.
Because that light doesn't have very good reflectors, I suspect you have around 80-100 micromols of PAR, which is high light. In order to use that much light you are going to be a very busy hobbyist - keeping a good high level of CO2 in the tank, keeping up with pruning to avoid restricting the water circulation too much, cleaning often and thoroughly, making sure the water surface has ripples over the entire surface, and, of course fighting off algae blooms as they occur. It would be a much more pleasant experience if you used just one bulb, to get half that much light.
I appreciate the input... now which bulb would be best to help with the plant growth... the 10k or the 12k bulb? currently, the light is set on a timer from 2pm-10pm. I've noticed others splitting their pp in sections. Is there a specific benefit to doing that?