> None of them made the switch back to C++ and their "prototypes" became finished products.

This is because the vast majority of the time people's claims of performance requirements are complete BS. If you're writing true system software (an OS kernel, a database, an MQ system, etc) then shaving microseconds is going to matter because 10s, 100s, 1000s or even more applications built atop or using your code will be leveraging the minor gains you are creating. If you're building "Misc App X" then it's probably not going to matter.