Hmm...

a couple of housekeeping type items - is Virtualization set in the BIOS? hyper-threading? how did your %CSTP look in esxtop?

Sometime more vCPUs != better performance depending on what you are running and how procs handles the time slices. Can you try these tests on a pool where the desktops only have 1 vCPU and see how your performance looks?