Is this https://phabricator.wikimedia.org/T68819 again? As an example, I prefer http://www.webpagetest.org/result/140527_0F_HE3/4/details/ JPG rarely get unwiedly, but it's very easy to reach multiple megabytes with a handful PNG and GIF files. On [[w:en:Barack Obama]], the biggest image (25 KB) is a PNG thumb of a SVG graph; the main JPG of the page follows. Do we have stats for 75th/99th percentile of image size downloaded upon article requests? In some popular pages I ended up converting PNG to JPG manually, to save some hundreds KB... maybe that's something worth doing on the fly. https://phabricator.wikimedia.org/T56291 is still open too.
Nemo