[xzyfer]

The priority queue isn't the issue. In fact the priority queue is what kept our first paint times tanking because browsers prioritised render blocking resources instead of images.

The issue was due to the variance of image size. An image that is significantly larger than the page average will be loaded slower since all images get an equal share of bandwidth (priority). Adding sharding wouldn't help since the client only has a fixed amount of bandwidth to share and all images would still get the same share of it. Sharding could help if the bandwidth bottle neck was at the CDN but that's rarely going to be the case.