Was just discussing this type of scenario with some reefing friends. If the "look" of the lighting system is not an issue and you want to grow high light sps, I would say that 400w moguls give the most light. 250w HQI double endeds are nice and sleek, but moguls (though an older technology), give a better spread and you can place one every two feet since each (in a proper pendant reflector) should cover a 2' by 2' surface area. I would also supplement the MH with VHO strips with good reflectors. Not crazy about PC actinics & many of us like the look & performance of VHO super actinics (perhaps mixed with some Daylight VHO bulbs too for enhanced growth). Whatever lighting setup you choose, be prepared for the "BIG" price tag it will come with. If you go with pendants, you're looking at 8 for a 96" by 48" surface area & maybe more for the 120" by 48". Hope you own your own oil company
Also, be prepared for a massive jump in your electricity bill.
Anthony