You may want to check out high output T5's with individual reflectors. It will probably cost you close to the same amount to start, but will save you electricity and heat in the long run. They are a little less "proven" and some people just like the look of metal halides, but they still might be worth checking out.
I don't know how new you are (8 posts so I'll assume new), but I think you definitely want to stay away from power compacts if you want to keep SPS. You might be able to keep some SPS alive at the top of the tank, but you probably won't get anything for growth.