Your test might be more realisitic; however, your original statement was 'The fastest way to use DBI is with prepare_cached() and bind variables.' which, as proved by the ealier posted counter-example, is false. That was my only point -- that there exists an input that causes your stament to be false, nothing more. Your statement would probably be better worded something like 'The fastet way to use DBI is normally with prepare_cached and bind variables' or 'The fastet way to use DBI is with prepare_cached() and bind_variables except for when it is not' ;-)
Like I said in my origional post, I am just nitpicking, being a pedant, as it were.