kdw75,
Xerox generally do not allow resellers to add a Fiery RIP to a pagepack device that was originally signed up without one. That is probably why your reseller is reluctant to talk about adding one.
To get the best speed out of the device you will need to look at the PDF settings (as you already have) and the settings in the printer driver. You will get the best quality with a PS driver, but you could look at using the pcl6 or xps drivers if quality is not paramount.
Whic of the 3 quality settings you use within the PS driver will make a big difference, only the high res setting uses the full resolution of the printer and is much slower than the standard setting. There are also settings for controlling the PostScript data in the advanced tab that can have a bearing on RIP speed.
The sort of work you describe would certainly benefit from a Fiery, the embedded Xerox RIP is designed mainly for general office use not graphic arts applications like VDP printing. There is a feature on the Fiery called freeform that would help with your workflow (i believe this was mentioned above). With Freeform you split the job into the static and variable elements and send them separately, allowing the rip to hold the ripped static data and then quickly process the variable.
The question is whether or not the time you would save can justify the high price for adding a Fiery.