Thank you for contacting the Intel Communities.
Regarding this, having 2 different cores working in your sever would allow you to perform more tasks at the same time.
2 processors would mean the double of workload the system would be able to handle. This doesnt mean that with one the performance would be bad, you would be still getting good performance with a single processor server.
Dual processor systems would help with email services also.
Also, here you can find a comparison of these two processors: