8x54w light is a crapload of light over a 90g tank. You'll not only be able to grow SPS with that light, but you'll not be able to grow much else in the top 1/2 of the tank unless they're under shade. I would suggest getting a 4 or 6 bulb setup with good reflectors (tek or otherwise, just make sure it's individual reflectors) and using the extra money saved on an upgraded skimmer or more flow in the tank. even 4x54w is a good ammount of light, but of course 8 is going to be more. The trick with T5s is always primarily the reflectors.