So when I started testing the soon-to-be-released KDE Plasma 5.x releases they were... less-than-usable on fglrx (and would fairly frequently fail to come back from suspend/resume), so I had to switch the laptop over to Intel graphics. However, since I need to be able to run OpenCL and OpenGL/GPGPU stuff on the laptop I switched back to fglrx on the weekend... and it pretty much works. The only real issue so far is with Chromium (i.e. not KDE per-se), where every scroll (and even typing) has a significant lag that looks like a compositing/buffering glitch. Likely due to multiple levels of using OpenGL for optimization, I'm guessing, may play with disabling OpenGL accelleration in Chromium for that.