From an efficiency standpoint the fewer motors you have running the more electrically efficient the system (and this applies to noise as well.) So I recomend that you buy one pump that will handle your design criteria (If you can afford that many computers I don't think you'll have a problem shelling out the extra for a "real" water pump (Oh and me,... my Eheim is in the mail... it is still just an aquarium pump
Tokamac