MaxClients of 100 seems pretty high to me. Commodity hardward isn't going to deal with 100 simultaneous mod_perl jobs very well! Even if you have the memory to handle that many jobs, you probably don't have the CPU.
MaxClients can be high on a front-end server which serves static content and does a reverse proxy to the mod_perl backend. Those servers do much less work per-request and a given machine can run more of them simultaneously.