I thought mysql used page locking? Which causes more conflicts than row locking. PostgreSQL is slower again tho, isn't it? The lack of transactions means mysql can be very fast, but it has a price!
My recommendation would be to move to Postgre for the ACID compliancy, which will save you headaches even if it's a bit slower, and limit the number of people who can access the db-driven pages at any one time - each load of the schedule page could check the current database loading, and if it's too high, reroute to a static "try again in a few minutes" page.
NB: I haven't used either database very much myself, or even installed OpenACS yet, so don't ask me how to implement that 😊
