If the reason you want to BCC 450 people is that you do not want them to see each other's addresses, have you looked at doing a mail merge?
A mail merge in ACT! can target the printer, a document or an e-mail. So, if you create a template (or edit one of the existing one that comes with ACT!) you can mail merge the information from your contacts and end up sending a personalized e-mail to each one. ACT! will send a separate e-mail to each of the 450 contacts, so they will not see each other's addresses, and because you use Mail Merge, the e-mail can be personalized.