That process is useful for determining overall resource usage, but won't help you much, if at all, for determining which of your PHP programs are consuming various amounts of resource. For that, you should review Getting PHP granularity in user resource reports.
The "basic metrics" I was talking about when referring to evaluating a page's loading time involve determining what part of the page is taking how long to load, and otherwise reviewing how "efficiently" the page is constructed and what might be done to improve it's loading time.
The FireFox Firebug extensions FireBug, Yslow, and Web Developer have numerous tools for checking on these things. There are many different things that can be learned about a given page/site's performance using these tools, and often you will be surprised when you learn where the bottleneck really is when a page loads slowly.