Extra Case Fans for Antec Two Hundred Case

I'm planning to use an Antec Two Hundred case for a digital photography workstation. Expect to use a 95-Watt TDP CPU on 785-based motherboard with the on-board HD4200 graphics (i.e., no separate graphics card(s)), a couple of hard drives and a DVD burner. The case has bottom power supply (will put in a 500 Watt modular), a 12-cm rear fan and a 14-cm top fan (at back of case). These fans are supposed to move 30-51 cfm (rear) and 34-59 cfm (top), depending on speed. Many sources suggest adding a pair of 12-cm fans in front of the hard drives at the front of the case. Question: how should I "spec" the front fans? Am I looking for some specific air flow rate to "optimize" the ventilation in the case, or do I just pick a pair of fans that are relatively quiet (since they will be near the front) and will move some air past the hard drives?