Don't worry about your impression. In fact, we use Moodle for both French Numeric University of Law, and University of Law in Toulouse (south of France).
We have 500 students in the first one's and 17.000 students in the second's, so i can say that we have already installed Moodle, and twice ...
But if you wanted to know configuration for high number of students from 3 years ago ... we don't have this experience !!!
I'll send you, in private message, the configuration we will install for 200.000 students at the beginning of 2007 ... if it can help you !!!
Happy that our comparison chart can help you for choice, even if it's an old work ...