If the folks are old shell script hands, I would pitch perl as a better shell language. In particular, if the project is ported to perl from the shell scripts, it will probably proceed faster than if it is coded from specs in either Perl or Java.

Off the top of my head guesses about performance, aren't going to help you. Run some timings of typical things your system does. If Java wins I'll be surprised, but if the margin is large I'll also be surprised. Java has had a lot of optimization attention over the years, I'm guessing some of that paid off.

Phil