Mag 9 would be a good choice. At 5' head height, it would be pumping about 634 gph
with a 3/4" return pipe... but if you factor in a couple 90's and a ball valve for added control, you'd be right at 600gph, and would have the ability to restrict the flow with the ball valve.
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry