There are still the odd applications for which a few CPU cycles per computation can add up to a rather significant difference, but these tend to be written in C, C++, or Fortran, not Perl

And there is a reason for that: if you need that kind of tiny optimization, you've already switched that part of the code to C or C++ or some other high-performance language weeks or months ago - those languages can easily give you a 1000% performance boost over perl with no changes in the algorithm whatsoever. Just compare the cost of a perl method call to one in C++.

But since perl integrates pretty nicely with C and C++ and is so much easier to code in, in general it's still much better to start out with pure perl, and only re-write the stuff that really does need to be fast in C/C++.

Update: that's to say that I generally agree with the OP, but I'm also working on a project that's already spending about as much on hardware as on programmers. Spending another man/month or two to decimate (literally) the hardware cost can certainly be worth it.