If you're going MH
then a 175 is perfect for your hex. 250's are great because of the wider variety of bulbs and it's a lot more light for not much more $$. PC
's will definately be OK for Mushrooms and Polyps, but very few people can stop there
If you're not in a hurry, I would suggest waiting for Spring and buying coral frags from fellow hobbiests. This has three BIG advantages.
1 - The Coral is KNOWN to be able to thrive in a captive environment.
2 - Is does no damage to the natural reefs.
3 - It's a LOT cheaper
I would like to remind Reefrunner what the Kelvin temp really means, but that's another thread I believe