I doubt anybody will be able to answer this for me, but it is worth a shot.
EsXi 5 on an HP Proliant G5.
Two ports from two physical network adapters - one Intel, one HP linked to a single vSwitch. The VMKernel port is on this VSwitch.
If I pull data from the server - to any of the three datastores, speeds do not go greater than 40-50mbit/sec. However, if I pull data from the server, I can get speeds of 200-300mbit/sec easily.
The network adapters and the switches (redundant Cisco 4506's) are both set to 1000 full. I have tried putting one adapter into standby (in VMWare), then the other adapter into standby, but the problem persists. So I know it is not a problem with the NIC's themselves. That also kind of eliminates the switches at the cause of the problem.