I recently replaced 3x96W PCs with 4x39W HO T5s and I'm very happy with the T5s. For about half the wattage (156W vs 288W) I get about the same visible brightness, if not a little brighter, and the color balance is much better (the PCs made things look a bit washed out). And even though the wattage is lower, from what I've read the PAR should be much higher, especially deep in the tank due to the parabolic reflectors. I don't have a meter but I'm guessing that is the case because my SPS are doing a lot better. Extra bonus is that they run much cooler than the PCs becuase of the reduced wattage, so my chiller doesn't come on nearly as often.
Larry