The real question is the application of your Virtual Machines in terms of whether 6 cores is enough.
I run VMware ESXi 4.1 on my Phenom 1090T workstation with 16gigs memory overclocked to 4.0ghz. I can easily run 8-10+ client and server VMs for testing purposes.
I don't run any high processor consuming apps like testing SQL server or rendering, I only work on system admin configurations (AD, WSUS, WDS) and my CPU utilization isn't even close to being maxed.
For production purposes, the 6100 series / Magny-Cours is obviously the more appropriate solution due to it's larger number of cores and memory scalability with a dual socket board.