T5 fluorescents use less power. I slapped a 4x54 watt T5 system on a watt meter. 232 watts of power used to create 135 UMOL's of PAR on the sandbed (18" under the water) of my 24" tall tank. That beat a 250 watt 14K Aquaconnect halide in a ROlll pendent that was using 260 watts to put 120 UMOL's in the same spot. It would take 2 of the halides to cover the same area as the T5's so that would be 520 watts.
If you want a lot of light you can run the T5's on an Ice Cap 660 ballast which overdrives the lamps. 305 watts used, 183 UMOL's of PAR at the sandbed. Even overdriving the lamps I got 14 months out of them before I replaced them and they still had a ways to go as far as intensity goes.
If you decide to go with the T5's make sure you get good equipment, ATI or D&D brand lamps, Ice Cap or Sunlight Supply reflectors and of course the right ballasts.