I was able to make it working with:
Then I got 60fps in Steam, but no image. After disabling the Nvidia overlay in the Gforce settings I had an image again but heavy framedrops. After setting Bandwidth limitation in Steamlink itself to "Auto" these were gone as well. Now Rayman is running with 60pfs, what results in no speed change of the game. Why the game reacts so badly on not having 60fps I did not found out.