I got an older i7-2600 CPU, 16GB RAM and newer GTX 1070 graphic card. BUT GPU acceleration does not seem to work since Lightroom CC was released. I have latest drivers on Windows 10, I have GPU acceleration option set in Lightroom CC, I have set GPU to be the only one to be used in nvidia control panel and, just fore sure, disabled integrated Intel graphic accelerator in Windows device manager. Using some tools like local adjustments or (and mainly) heal/clone brushes are extreme slow. In Windows Task manager, GPU load for Lightroom is always 0% whatever I do. Indication of GPU use never showed up by Lightroom CC process. Thus I think there might be an issue with GPU acceleration.