Speed wise npm@5 caught up a lot of ground. Iirc it was the same a while ago. However, I always felt like the release was a bit rushed. I sticked to Yarn too tho.
Yarn takes 12 seconds to install all of our node_modules, npm@5 (latest) takes over 12 minutes.
This made it completely and utterly untenable for our CI system, so we switched to yarn and shaved 12 minutes off our CI builds. It's been fantastic.
Old results from about a month ago:
https://twitter.com/bertjwregeer/status/887450964420055043
npm 5.3.0: added 1991 packages in 538.289s
yarn v0.27.5: Done in 58.42s.