What size pump do I need?

[Murminator]

Ok first some details I'm setting up a 90G perfecto reef ready with a 25G sump. The feed line looks to be a 1" 1/2 ID feed and a 1" ID return line to a split loc line nozzles all through 1 1/2 bulkheads. The tag on the tank says 700GPH. Now if I go higher GPH is it going to overflow the tank? It will probably be a little over a 4' head pressure. I want to go with a sumbersible pump I was thinking of a mag 9.5 but at 4' the head pressure is 800GPH will the overflow take it or will it cause a flood? or could I put in a ball valve to choke it down? dunno if this damages the pump or not or should I go with the Mag 7 that only has a 475 GPH head?
Please throw some idears my way I'm looking at getting a pump this week
Sorry for all the questions I new to all the overflows, sumps and pumps