If your TV supports 4kp60 then the best setup is to add "hdmi_enable_4kp60=1" to config.txt.
Set the resolution to 1920x1080@60 in settings/system/video, and enable the whitelist for any resolution/refresh rate combinations you care about (probably 1080p23/1080p24/1080p50/1080p59/1080p60/4kp23/4kp24/4kp50/4kp59/4kp60).
You will then have a fluid gui at 1080p60, and kodi will switch to 4k when required (i.e. video is 4k).