click perform effects with respect to RAM

[Gordon Lee]

> A little more info abut the setup, all three NICs are on the same PCI bus,
> which I believe is of the 33mhz variety.

33Mhz slots are typically only 32 bits wide.
I believe that most if not all e1000 cards are 64 bits wide.
Do you have a 64 bit wide card sitting in a 32 bit slot ?  
It would be pretty obvious because the back half of the card 
edge connector would be suspended outside of the PCI slot.  
Some makers say they support that, but it can produce undefined 
behaviour.  Frequent Tx hang/restarts might explain the low rate.

The system chipset can also make a big difference in performance,
although these numbers seem too slow to be explained by that alone.
ServerWorks in particular make a fast chipset.

> The two outgoing interfaces are
> connected by a crossover cable because they wouldn't actually transmit
> packets otherwise.  I don't know if that is relevant at all, but just in
> case.  I have no other equipment to which I can currently connect those
> interfaces for the same effect.

Do you mean that the two ports are simply connected to each other ?
If not, what exactly are they connected to ?

Another thing that can slow down rates (again not to this extent alone)
is the speed/duplex negotiated on the link.  To get more raw information
on what is happening at the hardware level, try this:

bash$ cat /proc/net/PRO_LAN_Adapters/eth2.info
  ...
bash$ cat /proc/net/PRO_LAN_Adapters/eth3.info
  ...

This will print the link speed and duplex, and the PCI bus speed/width,
among many other things.

It may be that there is a combination of issues that contribute 
to the slowdown.

    - GL