big pump, little pump ?

[iansfishy]

So in setting up the new tank, im wondering what pumps to get and where to apply them and I would like to hear from some pump and plumbing people. I already have a reeflo dart and plan on purchasing a reeflo barracuda. I planned on using the barracuda for my main return, because I have to go up from the basement about twelve feet and feed my refugium and frag tanks. I was going to use the dart for my closed loop which is going through a oceans motions 4 way, vertically about 4 feet. After doing some math, with water volume and vertical distance etc, would it make more sense to use the dart for the return at about 1500 gph or six times turnover ( through the sump) if i take it up to eight feet, and the barracuda as the closed loop pump at like 4500 gph for like 18-19 x turnover or even valve down the barracuda. I guess its better to have more flow inside the tank then actual turnover right? I never really thought about it until now. OR should I suck it up and buy two barracudas? Its only because a have to go up twelve feet to the main tank, as well as feed a closed loop. If anyone has better suggestions on diffrent pump options it would be helpful. there is about 240 gallons of total water, the main tank is a 180. thanks