Both of my forums (Mybb and NodeJS) run about the same speed on the same server. I haven't run actual benchmarks, but neither has appeared too slow to use. The Mybb forum has been around longer, so it has more posts and users. There was once I was I got DDOSed on the MyBB forum, and it didn't take much to take me out. The NodeBB forum has never had issues, and is a public forum and not closed off like the mybb forum.
The real advantage of NodeJS comes with it's ease of use of sockets. If you want instant updates, I see people building Node servers and connecting php to them for their instant updates. I don't see the reason for that, it seems ridiculous to have to use so many different technologies for your website. I was dead set on using Flarum once it came into being, until I saw this topic. http://discuss.flarum.org/d/534-community-chat-on-webpage-with-forum-usernames/5
It made me realize that PHP couldn't compete without using outside technologies with some of the instant functionality. I wanted that instant functionality, so I ran straight back to NodeBB. If you don't care about the instant live updating functionality, i'd say either technology is just fine.