As long as you have a good PSU, you can play games with that setup for sure. The 1080ti is still a capable card, and it may be held back some by the CPU, but if you play at a higher resolution, that becomes less of an issue. If you are truly ONLY going to be watching videos, a much cheaper GPU will still work just as well. The GPU, as long as it is fully functional, will have almost no affect on Video watching. You could use a GTX 1050, and it would look the exact same as a 1080 ti, if all you do is watch videos. If you edit/render videos, then the GPU makes a huge difference, but just watching videos you could go with a much weaker option and be perfectly fine. Upgrading to having a GPU at all might not improve anything either, because the iGPU in the CPU should handle that load fine. Try running your screen using only the iGPU, with no dedicated GPU, and see how it does. It might be perfectly fine. Unlike playing games, a stronger GPU will not make a video play at higher resolution, or details level. That will depend more often on the RAM, CPU, and your Internet connection, and if it is a downloaded video, your storage. In your case, if you do not have one, an SSD might be a cheaper and more beneficial upgrade than a 1080ti.