When you get into that volume, IMO, the tank volume starts to become a little more of a factor that drives up the screen size, because of turnover rate. You can only put so much water over a given width of screen before you start hitting a point of diminishing returns.
So what I would do is figure out your screen size based on feeding, then double it, and make it as wide as you can for the flow you have available. The more width, the more flow you can put across the screen.
We're kind of theadjacking here so maybe you want to start a new thread and I can help you with any questions on that....