I think I would go with more wattage just to give yourself a little more of a comfort zone in what you can keep in the tank. When I upgraded the lights in my 50 FOWLR
(was originally a FOWLR
anyway), I went with a 2 X 96 watt PC
fixture. I've now been keeping mushrooms and a condy anemone in there for several months and they are really thriving. I liked this lighting arrangement, so I went with a 4 X 96 watt PC
fixture on my new 90 gallon. That recently just cycled so I only have a couple of clowns in there so far. That gave me just over 4 watts/gallon in the 90, but I think that when you consider the difference in tank depth in my tanks, the 50 actually has more light than the 90 gallon.
You can skimp on the watts/gallon guidelines by careful placement of your livestock, placing the stuff that requires more light higher in the tank if I understand correctly, but I like not having to be super concerned about that. Just my opinion on it, but I like the 4+ watts/gallon as a comfort zone. All my livestock is reef safe in my 50 with the possible exception of my flame angel, so I've been considering adding some easier to keep corals in there while the 90 matures a little more and then transferring them to the 90 gallon. Will have to see how that goes. I've never done a reef tank before.