Hey buddy,

the QLE8042 is not on the HCL for ESX4.

There is a driver for 3.5U2 http://www.vmware.com/support/vi3/doc/drivercd/esx35-qla2300_707_vmw_7.08-vm60.html

If you are brave you can try to install the module on a ESX4 testserver(!)

Have you tried your tests with the normal mtu?

The socket buffer sizes you are using in the VM are quite small.

Could you try with larger socket buffer sizes:
netperf (or netclient) -l 60 -t TCP_STREAM -H <IP> -- -m 8K -s 64K -S 64K

-m is for message size
-s is for local socket buffer size : You should use larger socket buffers for high throughput networks (64K+ is better)
-S is for remote socket buffer size

If this helps, you could try modifying the default windows socket buffer size (MSFT provides some kb articles to achieve this.). This should help your file transfer apps.

Are you using Server2003 SP2. Because prior to that, Windows Server 2003 does not support TSO. TSO improves transmit performance (copying out of a VM) quite a bit. You could also try different VMs (64 bit version on Server 2003 SP2, Linux etc...) to see if your VM configuration is an issue.