Yea, generally you're looking at 3 or 4 feet to the tank. A Mag 5 would put you in the 310-380gph area.
With flexible line, you won't really have the bad bends that occur in hard pvc. I'd say a mag 5 would be fine for what you say you want. Put a ball valve on the return line to control flow. It won't hurt to dial it back slightly if you need.
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Frank
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