As I've fooled around with this I've run out of space for every part of the process: logs, database, test run outputs, the backup files, everything. I've separated everything into as many separate partitions as possible and that seems to help.
I'm using the generated jmeter test but I have added a progress bar block to a small course to see what happens. I want to add it to a large course and have all the test users hit the course page with the progress bar on it. I've found the progress bar hits the database pretty hard in real life. But so far I get a while screen of death trying to add the progress bar to a large course so I'm not sure having one user hit the progress bar on a small site will be enough of a stress.
I did a quiz at one point but that doesn't seem to use many resources. In real life we had a catastrophe when a large course was taking a quiz and many people hit the exam timeout time so all the submissions were sent at once. We had table-locking that went on for over 30 seconds, causing timeouts and freaked out students and professor (it was the final exam). I have no idea how to test something like that. Writing a quiz and a test that will have everyone submitting answers at the same time right at the quiz timeout seems a bit impossible.
So, long story short, the more I break everything up the better it works. I am currently running a test with 1000 users and so far so good. No heap space errors yet. No database or logs eating up all the space.