You can grow everything with metal halides. But the problem I had with them is the heat they put off plus the monthly bill you will be paying to burn them. I personally am a t5 guy so maybe some others will chime in who use metal halides still.
I run metal halides, my last set of bulbs I ran 3 years. No color shift or spectrum shift. I still grew sps so I think mostly there is a misconceptions about how long they last.
Two 150W bulbs would light a 75. Some areas may not be bright enough for some of the high light demanding corals, like many SPS. Should be fine for most LPS and softies.