Hi,
I use Premiere Pro and After Effect a lot for 4k video.
When I assembled my tower computer, about 6 years ago, I went for a relatively affordable graphic card, the Nvidia Geoforce 970, as I knew that Premiere at the time was not using the GC much.
It worked fine for some years, but over time Premiere and AE increased the use of the GPU, so I am now upgrading my graphic card.
I would not go for anything less than the 970, if you can afford it get something better