I do not believe there is any documented bandwidth numbers between sensor and FMC. This could vary per deployment based on the policies configured and data being collected. Also, for a vFMC, it depends on the RAM and CPU you allocate to the device.
Event database is 250GB for a vFMC. It is documented here:
http://www.cisco.com/c/en/us/products/collateral/security/firesight-management-center/datasheet-c78-736775.html