Hi,
There are a few I can think of that let you specify parameters etc. to test for, e.g. set and retrieve things on the page:

1. Flood - a profile-driven HTTP load tester
2. Performance test tools (list of)
3. Stress Testing an Apache Application Server in a Real World Environment - Which mentions Flood

As it's your app your testing, you know the parts of it that generate and except changes, new pages etc. so you can then at least get an idea if it's your code or your DB etc.

Lastly, I think there is more to this than just your Perl code, it's the whole lot:

• Web Server
• Operating System
• Operating System Tuning
• Memory
• Disk I/O and Configuration
• Bandwidth
• High Availability Clusters
• Caching
• Plus lots more.....

So depending on what factors you can check and change in reality, you might just start at the top, "Load Testing" and then work down.

But like I said, this is a whole other field with somewhat of a "Black Art" associated with it.
HTH.