Frankly, saying "We absolutely have no margin for error" is screaming "We need to have better plans for runtime error-handling." Perl can only do so much at compile-time. Are you saying that you don't have a simple hash-access with a variable? Nothing along the lines of if ( $foo{$bar} ) { ... }? Every single access is hard-coded? If that sort of safety is of such a major concern, you are using the wrong language.

That said, milliseconds is normal. Most webapps have a response time of more than 1000 requests/second. Have you considered using some sort of tied hash that would restrict which keys can be used? There's several implementations on CPAN for that sort of thing. The cost of tying is about 15% total. Almost nothing for your response time requirements.

And, error-handling isn't optional. Fast is worse than worthless if it's incorrect.