There's an old post (from 2012) here which might go some way to answer the question. You'll note that there are some major sites there.

Ultimately, as you've acknowledged, the matter is one of resources and network infrastructure and not one of software. No system will cope with 10K concurrent connections unless the network is built in such a way as to allow it.

Can EE handle Millions of Users?
I use Macs, Ubuntu, FreeBSD, OpenBSD, and Fedora for different purposes. I'm fairly busy and trying out a new distro takes a lot of time, but I hear lots of good things about Arch Linux from people I admire. I do mostly scientific computing (and some web development), and use Linux as both a desktop and a server. Does Arch offer anything I'm not already getting from one of my current installs? I'm particularly interested in the differences between Arch and Debian
