Use a benchmark utility like Benchmark.pm to get your figures. Using time on a Unix system is notoriously inaccurate for measuring differences in perl. I have no doubt that 5.8 is slower (it is, after all, doing more work with Unicode and all), but 50% sounds too horrendous for any developer to accept. My bet is that by using time, you're also counting the startup time for perl, which is probably significant considering how much more has been built into it. For those small 7-15 second jobs, it might take 1.5-2 seconds for perl to startup and compile everything it needs to.