The wisest thing to do is plan on hanging the light a foot above the top of the tank, then get a 2 bulb 24 inch long T5HO light (48 watts), and hang it that high. You should then have as much light as you will be able to manage, even with CO2. If you find that it isn't enough light, you can then lower it a bit to increase the light intensity.
fwiw I had a satellite 2x65 over my 29 before I tore it down. This was pretty damn high light I had to trim weekly everything pearled and if I didnt pay attention algae would explode. Definetly high light. I ended up running just one 65w pc bulb and still had great growth with pc. Pc fixtures are pretty cheap as well.