I purchased the new 5K iMac with the 3.5 GHz core i5, 1 TB Fusion Drive, and the M290X graphics card. I am not sure if I need this much computer, and I've never had a 4K/5K monitor, although I upgraded from a late-2013 MacBook Pro 13" with retina display. In terms of watching YouTube videos, and those that are recorded in 4K, is it worth it to select 4K vs 1080p on the 5K iMac? I don't know if I can tell a huge difference between 1080 and 4K on the iMac. I do select the "bigger" text scaling option, so I don't know if that negates any advantage of selecting 4K. What do you guys use?