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In order for you to have two processors installed they will need to have the same processor core stepping and the same exact model, these two processors have the same core stepping but the model is different and the number of cores, in other words they need to be exactly the same.
Also, I strongly suggest you to contact you sever manufacturer for better support as they are more familiar with your system and how all the components interact with each other. Maybe they will have different information for you.