A sidestep to optimizing: if you really want to get fast code, try to find out the pieces of code that are run most often (maybe with the Module Devel::DProf) and try to optimize the most often called functions, maybe even with translating them to C if possible and usefull.

In common, I don't optimize for runtime or memory usage; most of the time it is much cheaper to buy more RAM or get a faster CPU. Sometimes I just have to optimize, maybe because of certain borders like the memory border of about 2 GB/process with 32bit operating systems or the like.

Best regards,
perl -e "print a|r,p|d=>b|p=>chr 3**2 .7=>t and t"