Making Moodle quizzes to perform well on this kind of server farms https://moodle.org/mod/forum/discuss.php?d=214372 and at the same time not to tax a $ 7.99 shared hosting plan can only kill the module.
I know that the Moodle Team is working hard on a new caching engine for 2.4, so we'll see what performance gains we get.
The big problem with Moodle is that it has no queueing architecture. Why not have AJAX calls that check the queue for each request? If 300 students all press the ATTEMPT QUIZ button at the same time, why is it important that all of them get a response within 2 seconds?
I could see some students getting a message "Thank you for waiting, you are 230 out of 300... please wait" -- then allow Apache to process them sequentually.
I think Moodle is making educational instutions blow lots of cash on expensive hardware, when it could run fine by simply forcing students to wait to start a few seconds.