PHP script or database query to determine page themes

First, let me explain my situation. I had a web site with approximately 4000 pages. I have a default theme for the entire site and I am in a transition of changing pages over to a new theme. Well, actually each page is getting changed to one of three new themes. I have no issue changing the pages, i can do it based on the path or based on node-type. Once I get to approximately 60% of the entire site being changed, I would like to change my default theme to one of the new themes.

My question is, how can I get a listing of each node and what the theme of that node is? I will do it via a PHP script or database queries, which ever solution would be easier. My guess is that I would probably do a PHP script and use a function similar to what is used in the taxonomy theme module to determine the theme of a particular page. I just wanted to make sure that this would be the best solution.

I would love to hear anyone's suggestions on how to accomplish this the easiest way.

Thank you,
Shane