For a tank that size, T5 would be the best bet (in my opinion), especially with heat issues of metal halide. I have a 46 gal bow-front (This is merely a 33gal with a bowed front) with a Tek T5 fixture 4X39W and it allows me good growth for soft corals and LPS anywhere in the tank and minimal to good growth for some lesser light dependent SPS (Monti Cap and Monti Digi) when they are kept to the top 3rd of the tank. BTW, my tank changes temperature from 80 to 83 during the day when the lights are on, so there will be some heating with the T5, but not as much as MH.
What you need to keep in mind is, there are some corals that require a lot of light and others that don't. Prior to going to the local fish store (LFS) to pick corals do some research online.
Here is a picture of my tank with the T5s.
