Does anyone know where I could find reviews or reports on tasks that people implemented in two or more scripting languages to see which was more suited to a specific job? I want to know which languages are best suited to which types of operation so that I can make the most of them.
"Types of operation" could be sockets, the file system, logic evaluation, regex, or drawing.
I'm mostly interested in Python, PHP, Perl, and Ruby.
There's the programming language shootout: http://shootout.alioth.debian.org/ Although it may not measure enough of the things you're looking for.
However, benchmarks almost certainly won't tell you anything useful about high level ideas of the sort you listed. For those things, the performance (as in speed of execution) has almost nothing to do with what language the code is written in (at least for the set of languages you listed, all of which have quite similar execution models), and almost everything to do with how the code is structured.
If you want to be able to choose one of the languages you listed (for a particular task) based on something relevant, the questions you should be asking are:
Finally, if execution speed really is very important in your application, and if you find that you can't achieve the speed you need even with an appropriate choice of architecture in your chosen language, then you can identify the bottleneck and re-implement that in a compiled language, providing an interface back to the scripting language so it can be integrated into the application. All of the languages you listed support such native-code extensions.