You never gotta squeeze everything you can everywhere!
Regardless of how slow the language is, the 90/10 rule applies: 90% of the time is spent in 10% of the code. Optimize that 10%! Making the rest of the code faster isn't worth the code quality cost.
That's a rule that might hold for applications and services. It does not hold for languages and libraries, where any and every aspect is going to be the bottleneck in someone else's code. It's a different 10% for each user.
Regardless of how slow the language is, the 90/10 rule applies: 90% of the time is spent in 10% of the code. Optimize that 10%! Making the rest of the code faster isn't worth the code quality cost.