I think the 6 hour limit seems to work really well. Suddenly my estimates of when my job might start seem to be about right even when there were a rather large number of jobs running. Still with significant margins of error of course, but way better than the typical best guess at Louhi, which for a large job is something like "will probably start within two weeks plus or minus two weeks". It will of course get worse in production, but even so you will be reasonably sure that if you haven't run much lately, your job will start in about six hours. It also seems that large jobs start reasonably quickly, even when there are a lot of short jobs in line. I like these settings.
Thanks for the comment! Short queues make fair share really work, but restarting jobs often will cause some unwanted manual work and based on our tour at the universities there are still a number of codes that can't be run efficiently (or at all) in short queues. The queues will be longer in production likely with preference to large jobs.