For performance tuning, nothing beats having your hands on a working system.
A tool/language that is more effective for development can get you to a working system faster, leaving you more time to study and profile. And often times that's enough to win out over a more CPU/RAM efficient language that takes longer to develop with.
In my career I've seen Smalltalk systems win out over C++ systems, either by outperforming them or by actually finishing ("We could never have build this with C++"); and I've seen a 100KLOC Perl application server win out over Java.
Getting there first can give you a big advantage.