Please re-read Paul’s advice in post #3.
If you want to design a web site to fit a huge window, go ahead. If the size of the content appeals to users, they will return; if the size is “tiresome” or the content is pointless, they will not return. If you are trying to accomplish “responsive”, then you should be thinking of how the site will play on small devices, too, and how much of the content is wasted on big screens. IMO, use common sense. What size web site appeals to you?
About pixels and size:
One can find screens that are 1920 by 1080 pixels on smartphones as well as large desktops. Both screens have same number of pixels but the pixels are different sizes. Fortunately, there is a dots per inch calculation that helps the browser render the content at approximately the same size