Jeff - Lisa's insightful response made me think of something...

You say you are using 100Mbit Ethernet.  A gotcha in that area to
make sure of is that your adapter cards are not set for
Auto Negotiation: it is notorious for not working.  Too often,
one ends up with a conflict in duplex settings that results in
substantially reduced throughput, with Late Collisions showing up
in the ethernet adapter stats.  Your network staff "feels the
bandwidth is there", but that's theoretical and means little.
Unless all components of the network agree in their configuration,
throughput is hampered.  Just another thing to look at.
  Richard Sims, BU