You have my greatest appreciation for building proper responsive websites in all those links, with proper CSS styles and sizing (rem units)!
I use a 40" 4K screen (no HiDPI) and almost any other website, including the most popular ones (I just checked github, google, bing) do not really follow responsible principles, use px units, and end up using just a tiny column of the screen... and they are not even consistent: bing and google use the left 1/3rd of the screen, github the central 1/3rd.