Rays would prefer the extra width but the Lei would be better off with the extra length. Whats the cost difference between to two, I personally would go for the longer one, but it seems you have already made up your mind.
The price difference on the 96x48x24 and the 72x48x24 is $1200. I haven't gotten an estimate on the 96x36x24 yet. I still can't make up my mind. Last night I was thinking about what other dimensions and I came up with 84x40x24 which is about 350 gallons. Its hard to choose, because I don't want to make the wrong decision with the amount of money thats going to be spent.
If that's all it is. Hold off a little while longer. Save up the additional $1200.00 and get the tank your really want. With that size of tank and investment, it'll be worth the wait. You know I'm right.