parse vs execution time

Just wondering if there has been any discussions of parse time vs execution for a php page. In a project I'm doing at work, I have a couple relatively large php pages, about 20k, each with various functions that are conditionally executed based on input parameters. These pages are almost all PHP code, very little static HTML. A lot of SQL embedded in them. The execution time of any given path would be relatively low, but I'm wondering if the time to parse and build the execution path could start to become a factor for these larger pages. Would I be better to keep seperate execution paths seperated in different php files so the interpreter doesn't have to parse and build the execution path for code it will never run? Also, could the use of REQUIRE or INCLUDE help with this? IE: The manual says INCLUDE is processed for each time its encountered in the execution path, does this mean its not "included" at all if its never encountered in the execution path, a branch not followed? Also, I'm still using PHP3, haven't found the time to do an upgrade yet, Would PHP4 help in these areas? This is for a intranet, relatively small actual reply pages that I want very quick actions on. Brian