There really is no need to light a tank end to end... lights don't go straight down from the edge of the fixture. I'm running a 4' light over a 5' tank. A 5' light over your 6' tank should be fine.
Nothing wrong with T5's. They're certainly the least expensive entry for large tanks, and you KNOW, for a fact, that they'll grow corals. The right quantity, with the right bulbs, you can grow anything under T5's.
I do miss the shimmer, though. I'm an old Halide guy... Halides + PC, then Halides + VHO, eventually Halides + T5's... Awesome growth. Today, it's Kessel AP700's + T5's. You can get that halide shimmer, without needing a chiller (and an upgrade to your home's electrical service!) :D