That is a 36" tank If it is the same as my sump from Oceanic, I think 36"x18"H &18"D If I remember correctly. Depending on what you want to do with this tank I think the initial cost from 150's to 250's would be about the same. The thing you have to look at would be what are your plans now & future plans, I tend to say go with the 250's with smaller pendants even though It may be an over kill or over lap somewhat, If you plan of getting a larger tank down the road you could reuse them up to a 4ft tank. If you don't want to deal with extra power consumption, more heat & plan on staying with this tank a few years you could do one larger Luminarc reflector with a 250 watt over it, It should pounce the tank well with light but will have some over lap on the sides because of the size of the large reflectors & being square, If it can fit under your hood.