1 400W will work fine, don't worry. Your tank will be brighter in the middle than at the ends, but so what? On my old 45 breeder, a 36"X18" tank, I used 2 175W bulbs and the light was outstanding. If you do go with 250W bulbs, the only reason I brought up the T5s was for actinic support, i.e color. If you wanted to avoid any actinics, I'd suggest 2 phoenix 14k DE bulbs, and get the lumenarc DE reflectors