I have many systems with 4200 and 6200 CPU, but getting poor performance from benchmarking programs.
OS is Windows Server 2008R2 SP1 on it.
Please update Hotfix from Microsoft web-site and try again; Hotfix 2646060 and 2645594.
http://blogs.amd.com/work/2012/01/11/an-update-for-your-2012-scheduler/
When you use the Hyper-V then you need Hotfix 2568088.
http://support.microsoft.com/kb/2568088