How do you measure speed though? Speed to hit the done button or speed to get to production bug-free? You aren't really measuring speed accurately until you account for all the downstream time, and even include time for problems found in production. After all that, you need to account for any technical debt that was accrued as a result of going too fast to get this specific task done. Almost every day I run into a 1 hour fix that is now going to cost us 10 hours to recover from.

Are some developers faster than others when you include all these concerns? Certainly. But measuring it is so incredibly difficult and error-prone that we mostly just stick to some emotional impression of how fast someone is.

I was actually referring to the runtime performance of the code not time to completion.