> Sometimes writing faster code is the difference between using a hash instead of a list. Sometimes it's spending an entire day optimizing a function that's called once. The former is performance aware, the later is premature.

I disagree, it depends on the context. If using your original list is so fast that nobody human can notice the difference, it's a waste of time to turn into a hash, not "performance aware".

Actually, whether it's a "waste of time" also depends on the context. It could be worse. It could make your code harder to understand and maintain.