I have two SaaS products using this stack, and my personal site. The SaaS products get decent traffic (millions of requests every month, thousands of requests per-minute). I use Postgres for everything and I have no complaints.

I'm no Google, but it has been holding up very well (I've never had any issue with CPU, memory or anything). My simple release strategy does come with potential downtime, but the shutdown and start up are so fast it's very minimal.