OpenERP is relatively few years old. If I am correct, it is less than 10 years. Typically large enterprises don't upgrade ERP systems to major version often. It happens once in 5 or 8 years only.
Very large enterprises uses database sizes in Terabytes (TB)
Can you share your largest OpenERP database size you have administered and OpenERP version you have used?
Optionally you may share your server configuration? What is the Size of RAM, CPU, etc..