J.B.
When you are thinking about what wattage you should do with the halides, from my experience it has to do with the depth of the tank. If you have 80 gallon (and mentioned 48") that would make that sucker about 20" deep. I am not one to drop a bunch of money just to say I have more power. So I would say go with 2 x 150W MHs. That would penetrate the bottom of a 20" tank just fine.
If heighth is a concern in your hood, you could go with 4 x 39W T5s. Thats what I just decided on. They take up much less space and I picked mine up from ReefGeed.com for about $360 with EVERYTHING including an IceCap ballist.
But you are going to want to make sure you have enough space between your halides and the water (I would say 5-8"), and that you have plenty of air flow from a couple small fans in the canopy.
Good luck with your decision! -DIRT