> My argument has always been and still is...a language x written in language y cannot by definition be faster than language y.

While this may be true in theory, in practice it is often not true as usually there are time constraints.

Working in a low level language Y can take much more time & effort than a high level language X. This can mean you can profile and iterate the program design to improve performance much faster in X than in Y. Worse, if you have optimized a program in Y following algorithm A, it would be much harder to switch to optimizing following algorithm B. Because almost always "optimization" makes program logic more complex and removes clarity. Some time so much so that you may not even try an alternative! Such increased complexity can also happen in an HLL program but a modular program can often be rewritten more easily.