What type of corals do you see yourself keeping? LPS, zoas/palys, SPS, mixed reef?
If you go with 400W halides you never need to worry about "upgrading" again, and can keep any coral you like in terms of light. 2x250W would also work with florescent lights for actinic/dusk-dawn effect. I personally use single ended bulbs, lots of selection in terms of light spectrum and cost.
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I'm out. 
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