watts per gallon is a terrible way to look at lighting.
In my opinion, for a 75 gallon sps tank two 400 watt 14k halides in the lumenarc reflectors about 12-15 inches off the top of the tank would be unbeatable. the photo period would be shorter of course... i would do on at 12noon off at 3, on at 7 off at 11.
if you cant do that, i would put as many 150 double ended bulbs over the tank as possible. i would have a mixture of 10k, 14k , and 20k bulbs. i would have a crazy photo period where 20k is on form 11morning- 11night, 14k on from 1pm- 10 night, and 10k on from 3pm-9night. it probably wouldnt fit, but 3 of each bulb would be cool.... 2 of each would work too.
i think that having super bright light, suspended a little higher than normal over the tank is the way to go. i wish i had money, all i got is crappy odyssea fixture with 2 x 150 watt....