I did a study on this (N>100m) at a previous employer who had quite a lot of e-commerce traffic. It's sort of true but also a massive over simplification. The

I did a study on this (N>100m) at a previous employer who had quite a lot of e-commerce traffic. It's sort of true but also a massive over simplification. The relationship between conversion and speed is not linear. Some people are beyond help, and others already have it so good they only notice the most extreme degradation in performance. It's also hard to isolate confounding factors like users who have fast infrastructure tend to be rich and rich people buy more stuff. Making pages load faster doesn't give them more money to buy stuff. Overall faster is definitely better but the specific magnitude will depend on your customer demographics. In our case the Amazon 100ms saved = 1% more sales was close enough for a rule of thumb.