75 gallon or 90 gallon

[lastlight]

There's no denying you'll get more light to the bottom with 400 vs 250 w but that depends on a few things (some 250w bulbs destroy some 400 in terms of PAR). I'm running 20k 250w bulbs (much less PAR than your average 10 -14k) in a 27" deep tank and have sps growing (colorfully) on the bottom.

Brad's point is still true tho. I'd go with the 75 as well. It's a nicely proportioned tank. Before I went any taller in that tank size class I'd definitely go longer or wider.