Topic: Integrating: Use the same db or a separate one?

I've had PunBB running on my site for a while now on a MySQL database.  I'm currently designing a system separate from PunBB where members can submit reviews and the such to have saved in a database then published to the site - also via MySQL and PHP.  But I do plan to use PunBB's user table and login system, so my question now is, should I set up my site's tables on the same db as PunBB or use a separate one?

I see the advantages of using separate databases being
1) I can back up data from one db easily without necessarily having to transfer the data for the other
2) If I screw up my own system with buggy coding or insufficient security, there's less chance of my PunBB data getting screwed.

But I wonder if there would be significant performance advantages to sharing the same database.  Any advice?

Re: Integrating: Use the same db or a separate one?

You don't have to backup the whole database, you can backup just the tables with the reviews and whatever belongs to them.

Re: Integrating: Use the same db or a separate one?

That's true but still concerned about point 2 smile  Is there a noticeable performance difference in using two databases?  What route has everyone here who has "integrated" taken?