Thank you for your answer.
I have updated to the latest drivers (GeForce GT 750M 2GB GDDR5) and I am using the latest Lightroom CC version.
I try a reinstallation of the graphic drivers and will check if this solves the problem.
We will be waiting for your response.
I bought a Dell XPS15 with 4K touch screen resolution. Zooming and panning are just fantastic, even on 4K and it's an absolute dream you can do this on the touch screen.
However the brush is so slow it literately takes seconds before the brush stroke is visible. This seems a known adobe lightroom problem.
Yes this is a known problem that Adobe acknowledges. The usual solution is to do the brushing in Photoshop or Photoshop Elements and not in Lightroom.
When I dis-activate GPU brushing is fast but Zooming & Panning is slow. Neither settings are good then.
Yes, that is what Adobe has told us. Again, the solution at this time is to not do brushing in Lightroom.
I uninstalled the nvidia drivers, did a reboot and installed the latest drivers I installed before. Another reboot and I didn't notice any difference at first. I disabled the GPU in lightroom did some brushing and enabled the GPU again.
It fixed my problem! However it is still not lightning fast but do-able. Especially zoomed out (fit to screen) there is a 1 or 2 second delay before the brush is visible. Zoomed-in, the performance is much better.
I hope adobe can improve the performance in future updates.
Cried for victory too soon. Seems it is still slow. I prefer to switch GPU off. Zooming and panning doesn't refresh good the the brushing is much faster.