by John Jackson.
Mark, I've run into a similar problem and am tinkering with variables to see if I can find a solution. I'm dealing with much larger courses though, > 4 GB per course. I'll post here when I find a solution.
I used Bluehost for Moodle hosting some time ago, on one of their shared servers with an introduction level plan. At that time they throttled the servers when Moodle put a significant load on the server, meaning they cut back on CPU allocation, making it run ever slower. I found running a course with more than 30 learners resulted in unacceptably slow performance. Of course if you are on a VPS this should not be a problem, and that's what I'd recommend for hosting a Moodle installation.