If you're loading stuff into a database via DBI, bind variables are generally the fastest way. Avoid Class::DBI or any other wrappers, and look into the execute_array method maybe, to do the insert in batches.

If you can use them, look into the external loader utilities for the various databases - it might well be faster to output SQL strings from Perl and pipe them into mysqlldr, or use the parser language of bcp or sqlldr instead of doing the munging in Perl.