My experience with a Win10 laptop and an Intel HD Graphics 520 integrated card is, that OpenCL does work, although not with every version of the driver. The gain is modest and expendable, like 30 %, while, on the other hand, enabling OpenCL can harm the picture, at least in combination with some modules (like colour zones), when blown highlights can become black (also in the exported image).
(Un)luckily I am away from home and the laptop, but I will recheck this and try to make an useful report. It is a combination of hardware, dt version and driver version, so probably not easy to reproduce. In general, OpenCL should be disabled in this case, I believe.
On an old Win7 PC with a HD 7850 (2 GB) card, the difference is noticeable, like 3 : 1. No problems, big improvement.