As Ray Carnes has mentioned, you can scale up by adding more hardware.
You can also try the Heimdall Proxy (HTTP://www.heimdalldata.com/odoo) Pg-bouncer or Pg-Pool-II does not work for Odoo because queries are in transactions. The Heimdall Proxy was specifically designed for Odoo to handle transactions and data consistency. It can support connection pooling, query caching, automated Postgres failover, and Read/Write split with Strong Consistency. Query caching will give you the biggest performance/scale boost. We have seen cache hit rates up to 90% on Odoo.
The best way to assess Odoo performance on any given hardware setup is with a default install (including a default Odoo and PostgreSQL configuration file) using the demo data.
With a VM running under Windows 10 (3GB single CPU) it is noticeably faster to refresh than v10 and v11. Displaying the first 80 Sales Orders takes just over a second.
v11 was roughly 3 times faster with a default install and configuration than v10.
Custom modules can hinder performance a great deal if not written properly.
Something that won't take more than 10 minutes, and will show you how Odoo can perform with a default install over the web, is to setup a trial at https://www.odoo.com/trial
I followed some similar tutorials to improve speed. Odoo Backend in general has a good speed, what is slow for me is the Website, even though it's a simple site with only a few elements.
I am using now the developer tools and in the Network tab you can see exactly what makes it slow to load. So now I can see what is making it slow and where to improve the loading. (Most of the time is the size of the images)