jmclea,
There are many reasons why the response time may be slow.
Please check here for code that can be used to measure PHP Script Execution time. If this is a production system, just echo it into HTML Comments:
<!-- put this at the top of the page -->
<?php
$mtime = microtime();
$mtime = explode(" ",$mtime);
$mtime = $mtime[1] + $mtime[0];
$starttime = $mtime;
?>
<!-- put other code and html in here -->
<!-- put this code at the bottom of the page -->
<?php
$mtime = microtime();
$mtime = explode(" ",$mtime);
$mtime = $mtime[1] + $mtime[0];
$endtime = $mtime;
$totaltime = ($endtime - $starttime);
echo "<!-- Script Execution Time: ".$totaltime." seconds -->";
?>
This is one method, another method would be to use the "Performance" moitor to watch CPU, TCP, Memory, etc while executing scripts known to take a long time.
The idea is to find out exactly where the performance issue is. This does not seem to be hardware based (from what I can tell).
All and all the best method is to closely monitor the performance of the system and look at what happens when specific requests come in, i.e. HTML Only, PHP Script (small), PHP Script (Large), etc.