[contingencies]

Some things you didn't mention are domain resolution latency and caching, browser request parallelization, delivery protocol selection and reducing the raw number of content requests. Basically you are entering CDN territory here.

[nicolasbistolfi]

That's why I added the CDN part, didn't wanted to go to deep on that issue. As you're saying CDN it's a big part of the image delivery, even more important than having a great algorithm to compress those images. We've found that after passing a certain threshold, eg. the image being < 200KB the download time it's not something important, so the size doesn't matter that much, the TTFB (time to first byte) is crucial.

There's also a difference between performance, speed and actual perception of speed, but that is very hard to measure and maybe it's an issue for another topic.