I don't know which way it works out, but my answer is that it would be a horrible reason to not use strict.pm.

Sure, the (generally compile-time) checks that strict.pm invokes have to take some time. But the types of coding practices it discourages take more time at run-time. (Yes, it is faster to access a lexical variable than a global.) So it is hard to say which way the fraction of the second is going to go.

However there is no question that on any significant script you will save development time with strict.pm. And there is also no question that as a developer it is very important to come to understand that premature optimization is bad. So the question of how strict.pm plays out performance-wise is irrelevant to me, and should be irrelevant to any decent Perl programmer. The difference is small, it speeds development, and it assists in writing correct programs.

That is more than enough reasons to use it.