I just followed an example how to make libcurl and libuv working together. I removed usage of global variables and tested the performance by downloading (not writing to disk) 4.4GB file. It works great. It is comparable to my experience with completion ports on Windows.
The source code of my playground: https://github.com/amacal/peak/tree/5810adf59a026fc5f630e57791fc463f0452701c