We calculate the performance based on the EPS a VM with a certain number of cores can handle.
Please refer the specification sheet in the below URL to find out how much EPS an 8 core as well as a 12 core VM can handle.
https://community.mcafee.com/t5/Security-Information-and-Event/ERC-Capacity-Ratings/m-p/664323#M9739
The specification sheet does not mention 4 Core ADD-on capability for a 8 core ESM-ERC-ELM VM.
The max number of datasources that can be created on an ERC is 255.
This number can be increased by configuring child or client datasources.