To help people identify implementations or test cases that are slower than the others, maybe we should add an icon warning about it, with some explanatory title text or perhaps a link to a page to give advice on how to tune implementations?

If we're doing this, we'd need to decide what conditions warranted being warned about slowness? Slower by more than X% compared to the 'best' one? Slower by X& compared to the average? Slower than some fixed time (e.g. 1 second)?

There's no obvious candidate in https://doc.wikimedia.org/codex/latest/icons/all-icons.html but a quick literature review shows icons demonstrating slowness are generally either turtles or tachometers with the arrow over to the left, which might be suitable?