My guess without being able to query the system is that you've mixed NUMA nodes in your settings. The AMD 6212 would have been my last choice for a SQL Server processor today, the single threaded performance of those is substantially lower than the current Intel E5 series processors. The 6212 presents 2 NUMA nodes per socket, so you have 4 total NUMA nodes each with 4 cores and 8GB of RAM in your given configuration.

I don't know why you are using affinity mask settings here which are deprecated, instead of using ALTER SERVER CONFIGURATION (http://msdn.microsoft.com/en-us/library/ee210585.aspx) which is how you should be setting your process affinity per instance in SQL Server 2012. As Gail already pointed out, I wouldn't recommend setting a server up in the manner that you are doing here. If you want isolated workloads, make that server a VM host and run 4 different VMs so you have the type of isolation you are trying to get here.