I’ve built a small test page with several small images all around 5k. The test result for this (across the Atlantic, with DNS cached) is here http://www.webpagetest.org/result/151003_V3_SS1/1/details/
Several (5) of the early images always have a longer blue (content download) bar. If I build a longer page with more small images each also around 5k. The same thing happens.
So I am wondering if the longer blue bars are actually content download or in fact something else?
P.S. webpagetest.org is an amazing site , thanks for making it!.