64 bit vs 32 bit

I am getting ready to build a development server for one of our applications to host oracle for a client. The customer data set is huge and will take at least a month to load with large updates monthly after the initial data set. Our application is 32 bit but runs fine on 64 bit Windows. I am trying to figure out if we will see a performance gain by running on 64 bit Windows with 32 bit Oracle or 64 bit Oracle and Windows. If anyone has any real world comparisons, please let me know.