Hi Thomas,
are you using the X11 xshm or xvshm backend? Are you using the full 1900x1200 as resolution and/or xshm as outputtype? If so, the Atom has reached its limits.
I would recommend to set the applications resolution to a lower value and use the parameter "fullscreen" and the outputtype "xvshm" in the graphics section of the diskorc. In this case Disko will make use of the hardware accelerated stretching of the X11 XV interface. This should reduce the cpu usage of your application.
Attached you will find a sample graphics section for the diskorc.
I will take a quick look into the sources to see if we can get the text rotating. The CPU usage of the slider is dynamic. If there is not enough CPU to be had, it will automatically reduce its "smoothness", for example when a video stream is delivered in a root window as well.
kind regards
Stefan