It all comes down to how much bandwidth is available in your monitor's display inputs. It takes a lot of bandwidth to power a 4K display, especially once you throw HDR into the mix, and opting for more pixels often comes at the cost of a high refresh rate. For example, while HDMI 2.0 can quite happily support a refresh rate of 144Hz at 2560x1440, it's currently limited to just 60Hz when you move up to 3840x2160. DisplayPort 1.4, on the other hand, offers more bandwidth than HDMI 2.0, allowing up to a maximum of 120Hz at 3840x2160 with HDR - although some monitors will let you overclock them to 144Hz in their onboard menu settings. As a result, if you see a 4K monitor with a high refresh rate at the moment, it's only able to do so over DisplayPort. If you connect it to your PC over HDMI, you'll be stuck with 60Hz. The good news is that HDMI 2.1 monitors, which allow for 4K 120Hz refresh rate displays, are almost here. The world's first HDMI 2.1 gaming monitor, the Asus ROG Strix XG43UQ, will be arriving in May 2021, with more to follow later this year. DisplayPort 2.0 screens are also expected to launch towards the end of 2021, which will allow for 4K 144Hz refresh rate displays without the need for overclocking.