[rwj]

While I agree that implementations can be fast or slow, it does not completely eliminate the effect of the language. At minimum, different languages require different levels of effort to reach their optimum. So, while a language can be hurt by a poor implementation, it does not follow that all languages have the same potential performance.

As an example, just consider the enormous amount of effort that has gone into the JVM, and Java is still generally considered to be ~2x slower that C.