sswon1: I feel your pain.
I just upgraded to a 40B from a 29. When my 29 was initially running, it had an Eclipse 3 hood with 2x18W 5000K bulbs. No CO2. Plants grew lushly and rapidly -- despite the low wattage lights that were positioned too far forward on the tank; and the excessive height of the 29G which forced plants to grow rapidly to the surface to get the brightest light (making them lush at the top and spindly at the bottom). Algae was a non-issue, other than to occasion green spot I scraped off the glass.
Then I decided to go high-tech and retrofitted my hood to 65W HO and added pressurized CO2. Not only did my tank not get better, but it began to deteriorate. After a lot of effort to make it things flourish, I gave up. In the end, however, I made a very important observation:
Every day, as the sun began to set in late afternoon, sunlight would hit my tank directly for about an hour, bathing it in intense yellow/orange light. During that time, my plants would pearl like mad – even slow growers like crypts. They would Never do that with the aquarium lights alone, unless I cranked the CO2 up to dangerously high levels. In sunlight, the plants would pearl even when CO2 was turned off.
So, I concluded, the key -- or at least a very important factor -- is that intense light in the yellow to red spectrum made my plants happiest. I simply could not argue with what I observed every day.
Therefore, my current 40B setup will continue low-level CO2 injection with a quad T5 lighting fixture and a mix of 5000K and lower color temp bulbs, to reproduce the color and intensity of late afternoon sunlight as closely as I possibly can.
I would suggest keeping your double fixture since a single 39W might not be enough on a tank as wide as a 40B. (It is also much easier, and less costly, to switch off one bulb than add a second.) Even with the 2 bulbs, you might observe tall stem plants bending sharply towards the middle of the tank to reach the most intense light (assuming you place the light fixture in the center).
If the need for CO2 is a big concern, perhaps consider slower growing plants that are not as dependent on it.