I've got an LG 52x24x52x IDE cd-burner on hdc.
I've run k3bsetup and set both read and write speed to 52x.
However, when I open the cd-burning dialog, I can't select any speed faster than 16x.
This is something you should take up with the k3b maintainers, as it sounds
most like a bug in their software code.
Fixed in 0.10.