each user comes from the same IP. We have 5 load generator servers, each a physical box, so at most we have users coming from 5 different IP addresses. However, every "user" on each load server will have the same IP.
I don't think we need to persist client to web or web to app requests as the database on each web server tracks the activities of each user, but maybe I'm misunderstanding the question.
The load testing tool is built into the browser (Internet Explorer). The tool opens a real browser for each user. So, when there are 50 instances of I.E. running on 1 machine, they are all reading from the same cache pool. If I can find a way to create the unique cookie names, it would only take an hour or so to throw a load test together and test it out.