> I've heard many times that it is best to minimize the
  > amount of Python code that executes in the critical 
  > paths of a program; instead, we will get better 
  > performance by using native libraries (like the re 
  > module).

Keep in mind that, while the 're' module itself may be written in C, it is in effect an interpreter for another language (regexps). You can easily build a regular expression that will happily backtrack and capture its way into a performance black hole, esp. since you can't trace the individual sub-patterns using normal Python profiling tools.

Benchmarking the two implementations, as you suggest, is of course the only way to be sure in your case.