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That gives you 6.1 watts per gallon which gives you a wide virity of corals to go by but if you wnat to really kick it up and leave your options for coral endless you should go with about 8 watts per gallon. But if you just want soft corals or just even live rock yes what you discribed above is more than good.
I'm guessing that the 75g is at least 20" deep? 2 175w MH plus 110w pc should be fine. You may want to check hellolights.com for a combination on pricing. I wouldn't worry about the wattage per gallon so much. It really just depends on what you want to keep. Just let us know what type of corals you want, and we can give you our opinion on what you may need. HTH