I'd like to be able to send the user to another site (_blank) or (_top) after completing the form.

but targetting does not seem possible.

Actually, the default does that and creates a blank page with a thank you on it.

You can setup a specific page if you want. On the right side is a link to the settings. Click on the second tab, and on the right side, you can change the created thank you page wording. On the left side, you can redirect to a web page you already have (or build), or in the box below that, you can enter the html for the thank you page.

Do a search on the messages here, and you will find one message thread that has a tutorial describing how to create a page.