you should have at least 1,000 gallons of water running through the sump, in my opinion. get a 1,300 gph pump, to adjust for the height difference, and maybe put the water coming out of 2 or three jets.
Will this be a reef ready tank? If so the standard reef ready tank use a megaflow kit nowa days. The kit can handle upto 600 GPH. You can add more flow with power heads or a closed loop. Depeding on how many things you will have plumbed inline (UV, chiller etc...) you will know what size pump to purchase.
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My tank is like whiskey it gets better with age!