I have been testing Krita since many years now: mostly on Windows
As compared to Gimp 2.8.20 Krita should be faster as regards zooming and panning since you can choose to handle them with OpenGL (via your graphic card). However, I don’t know whether Gimp 2.9.X is better in this regard…
Krita has often been reported to being faster on Linux as compared to Windows (I have read it is due to the faster file system available on Linux).
All in all, Krita has been always developed to satisfy painters needs (not photographers) and, to my knowledge, very few painters are still using Gimp for this task. For instance, because on Windows the GTK 2 support for tablets is quite buggy currently.
At present, Dmitry Kazakov, a russian Krita developer, is working hard on adding SVG support  which, again, is a feature lacking with Gimp (I suppose it wil not appear with Gimp in the future either due to their shortage in manpower)…