I run 4 60" T5s (overdriven w/icecap 430s) over my 27" deep 250gallon. I also have halides, but only run them for 2 hours each day. I have no problem with sps and clams. I even have one acro on the bottom edge of the tank that is doing great. Low-light corals like mushrooms don't seem terribly happy in my tank, and coralline bleaches off of the horizontal rock faces.
I'm pretty convinced that T5s put out a lot more light than they're given credit for. Some data that GrimReefer posted in the equipment forum suggested they have better PAR at depth than T5s - probably due to the design of the single bulb reflectors.