If I choose 'Scaled' for the resolution, the only options are 1080p, 1080i, 900p, and 720p. I've plugged in my Seiki 39' 4K TV (SE39UY04), but when the 'Best for display' option is chosen, it outputs 1080p, rather than 2160p. Based on Apple's documentation, my Mac mini (Late 2014, mid-range model with Intel Iris) should be able to support 4K video through HDMI.
