A 40 breeder is only 16 inches high, but 18 inches front to back. The 18 inches pretty well forces you to use two bulbs, separated as far apart as you can, up to 8-10 inches. The 16 inch height means a 4 bulb T5HO fixture will give you about 300 micromols PAR at the substrate, and much higher up near the water surface. That might be good for a reef tank, but it would be a major problem for a planted tank. (The 300 micromol data is from TEK and Catalina fixtures.) A two bulb fixture gets you about 200 micromols of PAR, based on Archaea and Ice Cap fixtures. That, too, is possibly good for a reef tank, but not a planted tank. Raising the 2 bulb fixture about 8 inches above the tank would drop the PAR to about 100 micromols, which is high light intensity for a planted tank. Raising the 4 bulb fixture about 16 inches would also give you about 100 micromols of PAR.
I think most people using fixtures like that for planted tanks are hanging the fixtures above the tank, and raising them to reduce the light to manageable amounts. I know that Tom Barr does that routinely now - and he doesn't start with nearly that much light.