I've been messing around the the data from the 12/31/2008 PDGA Course Directory, finding the shortest paths that hit enough disc golf courses to play 400 or more holes.
Guess where the best results were, then go here to look:
I know it's a little out of date, and the "miles" I calculated are direct, not driving miles. There may also be some courses that don't have the proper longitude and latitude in the directory. So, if anyone seriously needs the information, it will take some more work.