So there are lots of things to consider before everyone get into a performance battle let me suggest you something in my perspective.

I have started coding back-end when I was 13 with PHP then I learned Ruby / Rails with Node Js

My PHP Experience: It was a real trauma for me, I always felt something wrong when I wrote PHP, it's absolutely very easy to start but you feel something strange when your code is working yet you do mistakes. I always felt that I'm a total idiot and never going to be a real developer, PHP was a fucking disaster for me, yet I should mention that PHP isn't the same PHP through my time, it developed itself thanks to Symfony community, but I still didn't like PHP because of the trauma.

Ruby Experience: Before I start Ruby and Rails, I have already used sass, stylus, jade, gulp, grunt these tools were popular at the time and I liked them a lot especially stylus and gulp which was I still use, anyway when I start Ruby first thing I have noticed was ruby was a source of inspiration for lots of tools in the ecosystem, ruby has a soft, beautiful syntax, and you can do solid projects or prototypes within hours with rails.

Node Js Experience: I consider Node Js at very different state, for me ruby is a nice sweet tool but node js is something alive, it's everywhere while you're on working, fucking crazy thing, for example when you develop web-app with node.js you can send response to both terminal (bash, command line) and browser, this feels very aesthetic and easy as hell, I have used Node Js to create lots of command line interface's which helps me while I'm developing something, yeoman-like tools saves your lots of time, Ruby can do that too but when you use node trust me, it feels different.

My advice for someone who's only getting into back-end first time, first fuck the performance combats, you need to love the language that you're going to develop, Python is a really fast language but that doesn't mean ruby isn't or node.js isn't, don't approach combat battles like ohh this language is really fast I should use it! performance is up to you as well, in the end know that. If you need something really fast then pick a language fits your needs. You need to love the language because back-end languages are ugly, time-consuming things basically you interact with a child who has a reptilian brain. For example, if you want to send this child to a market you have to give it direct instructions like go to north 5ft then open door by pulling the doorknob which was at x: 1435252, y:125435 then go to 15ft etc. etc. this is back-end programming at basic.