Q: php4,cache,performance,mod_perl,zend cache, APC

Hi, As you might gather from the subject, i'm trying to make a decision. Before that i'm doing research to find out what best fits. My question is; From what i've read php4 does post-compilation caching, is this right? If so, what is the point of Zend Cache or APC (Alternative PHP Cache)? I know from experience that mod_perl does copy and run from a compiled version of the script into memory. From the description of Zend Cache and APC they sound like the equivalent for php4. I guess what i'm getting at is is php4 as fast as mod_perl or do i need something like zend cache? also, is there anywhere with stated benchmarks that i can see to compare? Thanks, joe