Working with a customer that was having issues with writing data to a database that was stored on a Win2003 server we discovered the following. He was willing to install WireShark in his image/guest, and on an identical workstation/client with the very same software and same interaction. There was a profound difference in the response/performance in the two systems. He provided us with the WireShark output (performed at the same time..same traffic load) and I had our network engineer study/compare the output from both systems. Here’s what he realized: When it detects a slower (virtual) client, it lowers the priority of the requests coming from that client so that the slow connection won't slow down other clients with faster connections. To put it simply, the network is prioritizing based on connection speed, and that may be what we are seeing.
Here is a link to information regarding re-prioritizing communications between nodes
Change network priority for communication between nodes