The admin/tool/generator/maketestplan.php tool does not do quizzes unfortunately . It does do forum posts and I think that has similar hits on the database. Correct me if I am wrong.
All my load testing shows logging in and logging out to have the least impact in response time. This is especially true if you are using memcached/memcache for session handling.
We used the tool to create the basic course and test plan and then embellished it ourselves on a stand alone instance of JMeter. You can get JMeter to pretty much simulate anything, submitting answers, uploading docs etc. You just need to use the jmx file it produces and load up with a copy of JMeter http://jmeter.apache.org/
You then need to decide what you are testing, is it performance of specific activities, before and after type testing like upgrades, or seeing what load your system can handle. And then edit JMeter settings accordingly for target throughput, number users, loops of test etc
Mike