Odoo is the world's easiest all-in-one management software. It includes hundreds of business apps:
CRM | e-Commerce | Accounting | Inventory | PoS | Project management | MRP | etc.
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..
This is an interesting topic. Perhaps OpenERP Management should address this question as OpenERP claims they are Enterprise ready.
Based on my google findings, OpenERP does has performance issues with older versions. I am not sure it is addressed now. Here are some links on performance issues reported and some key people acknowledged.
As far as PostGreSQL is concerned it is well proven beyond any doubt. www.postgresql.org/community/survey/26-how-large-is-your-postgresql-database/
Hope OpenERP Management address this? or Community shares their findings.