return pump size

[crsaz]

So I want to run 3 tanks(all tied into the same system) off of 1 return pump and I cant decide between the dart 3600gph(2400gph after head loss), the barracuda 4500gph(3500 after head loss) or the dart gold 4300gph. The main tank is going to be 280g with 2 75g frag tanks tied into the main tank. which would you use and why?

I also have a few Q's pertaining to return line size. I have been told if I up the return line 1 size it will let the pump "breath"(best word I could think of) and ultimatly pump more water is this true?