A Radeon RX 580 Series GPU isn't brilliant but is a solid last gen card that will have no problems with Sims 4 on Ultra with uncompressed graphics. Sims 4 is not graphically demanding. It's really only Intel integrated graphics that struggle with Sims 4. I've even run Sims4 on a 11 year old ATI Radeon HD 5670 card (way less than the updated recommended spec) on Ultra with uncompressed textures for a while after my NVidia GTX 960 died and it ran fine.
EDIT: For comparisons sake, a AMD Radeon RX 580 is better than a Nvidia GTX 960, but not as good as a Nvidia GTX 1060.
