I like the tutorial, but I don't know why you would use PyQt these days. Tkinter is more permissive and has wrappers like appJar which make it disgustingly easy to put together a quick, ugly GUI. If you're building a desktop app that needs to really look good and be fast, why are you using Python?
Why not? For an app to feel fast, you need to make it responsive and non-blocking. You can easily make apps with Python and Qt or Gtk that start instantly and never seem to hang. Discipline when it comes to not running things on the main thread, using proper async techniques etc. is more important than the number crunching ability of your programming language.
And when you need raw speed, you can easily drop in some C++ code with SWIG for example. For example, I made a GUI for controlling an experimental sensor system. The GUI could look boring, but should be rock solid and always responsive, it should be easy to add new features, and it had to read data from PCIe at hundreds of MB/s or even faster. So I wrote the GUI in PyQt, the PCIe part in C++. Python allowed me to mock the hardware code out easily so I could test the GUI separately, and made it really easy to read configuration files etc. which is unneccessary painful in C++.