Two 54 watt T5HO bulbs is enough light for a standard 90 gallon tank, but not when they are spaced close together as they almost certainly are when it is a two bulb fixture. My choice would be to sell the 65 watt PC fixture, and buy another of the T5 fixtures. Then hang them above the tank so they are a few inches apart, and raise them 6 - 12 inches above the top of the tank. That would give you good uniformity of light in the tank, and enough to grow anything too. When you hang the light several inches above the tank you get away from having an insanely high light intensity up near the water line, while having just enough at the substrate.