We get between 300 and 500 rpm depending on the time of the day, all of which is served from a 8GB DO droplet running 4 Unicorn processes. Our forum (we use Discourse) also gets similar traffic, it is hosted on a 4GB droplet.

Wow, here's me thinking that you would have separate servers for database and web server and load balancers. Gives me faith.

We actually have the architecture in place for that, it turns out it was completely unnecessary. (See: https://github.com/hummingbird-me/ansible-deploy)

The application layer is completely horizontally scalable, all I need to do is edit the config file to add or remove servers and run ansible.

We see around 200K uniques per month. This month will be a bit higher due to HN traffic. We're running this on a Digital Ocean droplet and AWS for our media. It's a surprisingly simple set-up, really.