This message was posted on behalf of Intel Corporation1 of 1 people found this helpful
First of all let me tell you that both processors are compatible. You can double check this on the following URL going to compatible products at the left: http://ark.intel.com/products/56333/Intel-Server-Board-S2600CP2
About the mix it is not recommended/validated according to the technical product specification. Even thou it could be possible the performance might be unstable. Go to page 27 under the “Processor population rules”. http://download.intel.com/support/motherboards/server/s2600cp/sb/g26942005_s2600cp_p4000cp_tps_rev18.pdf
Hope this helps.