Thanks for the input.
One thing I have since noticed, sorting included files by size, is that Math::Pari comes with a huge 6MB shared object! This is bad enough, though not of course PAR's fault; but it is made worse by the fact that I have several instances of my program running and apparently an .so embedded this way cannot be shared. So the effective difference between a PARed and unPARed version of my program is dramatic indeed.
In my case, I might be able to get Math::Pari deployed separately. I think adding "look for large shared objects" can go in the FAQ, which is indeed otherwise useful.