Performance is often misunderstood... most frequently performance issues come from 2 sources... (a) database access, and (b) file system access (like writing logs). What's important to note... neither one of these is related to a particular language. Caching and data pre-preparation go a long way to resolving these issue.

Keeping processes resident in memory also can be a big improver of performance... you aren't going to get a clean comparison of JSP to straight CGI if you aren't using mod_perl or something similar.

Perl does a lot of jobs well; I think it is much more suited to 'batch' type processing than is java... for example, grab some data out of a database, drop it into an XML file. You then pass that file through a XSLT filter(s); get out some pregenerated HTML, marked up with a bit of javascript. That tends to be seriously scalable... and easy to support and debug. 'Use the right tools for the job at hand' is what I would have told them; sometimes that tool is Java and JSP... but often its not.