To stop that thread, here's the probable explanation. The firewall is a Dell 650. Dell 650 and 750 have two PCI slots. One is PCIX 64bits 133Mhz. The other one (where the fiber NICs are plugged) is 64 bits 33 Mhz. *this* is probably the bottleneck. Really a big, big, big thank you to brad@, henning@, mickey@ and theo@ for their wonderful help on finding this.