The apache flood project has exactly what you want. You can set up different actors to take different scripts on the page, if your page uses sessions or anything like that, you can setup regex's to pickup the sessionid's and use them on the rest of the site.
It also allows you to install flood on multiple machines, and run a distributed flood system, with the primary flood process bringing back all of the timing info.
http://httpd.apache.org/test/flood/