opc.three (12/24/2012)
It should say "physical cores" instead of "physical processors." I would set it to 6 for the number of physical cores per NUMA node. If you're still seeing too much parallelism for your taste look into increasing the Cost Threshold for Parallelism.
1) physical cores is the MAX you should EVER set MAXDOP on NUMA hardware. Don't leave it at zero either.
2) if you can, test your server with Hyperthreading disabled, especially it if is a data warehouse box (or possibly mixed-use server).
3) I never, ever leave cost threshhold for parallelism at 5 for any client I do performance tuning at. It is universally an inappropriate number for modern hardware. It should be larger. I do analytics to try to identify a 'best start' value for each client's server, but without further information I might try 15 for an oltp box and 40 for a DW box.
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service