This very much depend on individual image, how much detail and colors are there. Some compress better, some worse. It's good to lower the Jpeg quality until you start to notice visible artifacts.
But here is a trick: Highly compressed but high resolution, always looks better than less compressedd lower solution. I.e 1920px at Jpeg6 will look superior to 1280px at Jpeg10, even if they are at same size, let's say 500 KB.
But don't look at your visitors statistics...it's depressing. Half of people use mobile, and 90perc. of those have 320px displays. I don't know where all those iPhones8 and latest Galaxy users are...