A query to isolate top ~3% of desktop pages by page weight:
SELECT rank, url, INTEGER(bytesTotal/1024) as TOTAL, INTEGER(bytesHtml/1024) as HTML, INTEGER(bytesJS/1024) as JS, INTEGER(bytesCSS/1024) as CSS, INTEGER(bytesImg/1024) as IMG, INTEGER(bytesFont/1024) as FONT, INTEGER(bytesFlash/1024) as FLASH, INTEGER(bytesJson/1024) as JSON, INTEGER(bytesVideo/1024) as VIDEO, INTEGER(bytesAudio/1024) as AUDIO, INTEGER(bytesOther/1024) as OTHER FROM [runs.2015_12_01_pages] WHERE bytesTotal > ( SELECT NTH(97, QUANTILES(bytesTotal, 101)) as cutoff FROM [runs.2015_12_01_pages] ) ORDER BY bytesTotal DESC
On quick inspection, most of the outliers are due to lots (or heavy) images, or large autoplay video files:
Running a similar query against mobile data yeilds:
Almost all of the mobile outliers are explained by lots (or heavy) images.