Hello,
Are you referring the actual Net Express 5.1 product or its runtime (aka Server for COBOL 5.1... or simply Server 5.1)?
If it is the actual Net Express 5.1 product, the CPUs and cores are irrelevant to the product.
If on the other hand you are referring to Server 5.1, then I suggest you call your local account manager to discuss and review your license requirement.
Regards,