Not sure if you already did this or not...
There is an additional download for the Catia v5 reader for Workbench. When you run the installation script for Workbench, it asks you what CAD plugins to install. By default Catia v5 is not listed. In order to list it, you need to download the ANSYSCAT5110_WINXX (depending on if you're running 32 or 64 bit). After you run that, then run the Workbench installation script and you'll see Catia v5 listed.
In my personal experience, Catia generates HORRIBLE iges files. They are usually so bad that Catia can't even read them back in. Definitely go with the parasolid format if you can.
Good luck,
Doug