I went from 2x96W PC's on my 36" tank to 4x39W T5's and it is a lot brighter and I do have a lot better growth. Plus it's 4 bulbs, not 2, so I have a bit more flexability when it comes to how much blue and white I have in the tank.
For output without a reflector, T5's and PC's are fairly close, but the reflector is what sets T5's apart. The proper reflectors are M shaped.
If you're looking for a retrofit kit (one that will be hidden in a canopy), check out
www.saltwaterconnection.com. That's where I got mine from, and I'm really happy with them. It's an all in one uint, the endcaps are mounted to the ballast and the reflectors just clip onto the bulbs. If you're looking for a fixture, check out
http://www.prairiereefsupplies.ca/index.php?id=95