<VirtualHost ...> PerlOptions +Clone PerlInterpStart 2 PerlInterpMax 2 </VirtualHost>
This might be worthwhile in the case where certain hosts have their own sets of large modules, used only in each host. Tuning each host to have its own pool means that the hosts will continue to reuse the Perl allocations in their specific modules.
When cloning a Perl interpreter, to inherit the parent Perl interpreter's PerlSwitches, use:
<VirtualHost ...> ... PerlSwitches +inherit </VirtualHost>