i would say CPU You need a good CPU that does not overheat for given high performance if it did , in the middle of the game = frame drop however you still need good GPU just make sure that your CPU does not bottleneck your GPU
It honestly depends on what your primary workload is. So it's important to understand whether your main workload is CPU-intensive or GPU-intensive or both. For example, many people mistake Adobe Lightroom to be graphics intensive since it's a photo editing software, but it's actually CPU intensive. In this case if you get a crap CPU with high-end graphics card, it'll still crawl. Premier Pro on the other hand would be straight-forward graphics intensive.