William,
This is very specific to your courses and I am not sure this is the same for everyone, but you make some important points. The optimal course ratio can very greatly based on the type of course, the method of delivery, the assignments and interactions included, and much more. There is no ideal, but many people report a range of 15-20:1 for most classes to be able to provide the right amount of feedback to students in a timely manner while still allowing for dynamic discussions to take place in discussion forums, etc.
Herbert Brown III
