like you said another guest works fine,
I dont hink it's the host.
the problems on teh 2003 may not have been hardware related, but rather software, and those were virutalized as well.
Possibly, but we never saw performance issues like this on the physical server. Everything ran fine. It was just an occasional blue screen that (supposedly), per the error message, pointed to some hardware fault.
Looking at the setup of both guests the SCSI controller on the 2008 guest is an LSI SAS controller. The controller on the 2003 guest is the LSI Parallel controller. Searching shows the parallel controller is prefferred unless you are using MS clustering, which I'm not, so I tested using both on the 2008 guest. Interestingly enough, and it could have just been a coincidence, but using the parallel controller on the guest actually seemed to give me a better trasnfer time on a test transfer of a 9 GB PST file over the network. So, in other words, that doesn't seem to be the problem!
Yea... more investigating.