You may experience that your XPS 9550 or 9560 laptop throttles the CPU. (It happens if both the CPU and onboard GPU sit at 100% load for a sustained period.)
This is NOT an issue with the laptops hardware or software. This is the laptop working as designed.
The XPS 9550 and 9560 laptops shipped as the latest, thinnest, and lightest laptops that Dell sold with the latest technology available.
Due to how thin and powerful these laptops are, the design combines the CPU and onboard GPU cooler into one unit. If both the CPU and the GPU reach a100% load, and sits there for sustained periods of time. The laptop throttles the CPU in order to ensure that it does not overheat. (Even while it is still capable of handling heavy CPU and GPU computations.)
You should look at a more specialized Precision workstation, where you require a device that can sit with a sustained heavy CPU and GPU load.