135g over flow/return question

[wannareef1]

I just got a 135g with 2 corner over flows with 1" bulk heads, and 2 1" returns about a foot in from each corner , I was told they drain about 600gph each, what size pump would you recommend, one pump or 2 smaller pumps, one for each return or one for both, the returns are about 6 to 7 feet head height, or from where the pump sits to the top of the return bulk head. what would you guy's do or have down, I'm sure somebody has done this already for a 135g or 125g, the tank is 72L x 18W x 25H, just incase you need that information

Thanks