I did 6 on, 1 off- one of my co-residents did every Sunday, I did every Saturday (whereas the other residents did the 12 on/2 off thing)- it fit us, and it fit them- it's all abt preference.
If the service component of the residency is pure staffing (ie no on-call issues, formulary approvals, managerial issues, etc)- an 8hr shift goes by quite fast. I would staff my Saturday, and then just work the rest of the day in the office on the next week's readings and get a leg up on projects/research, then Sunday was my complete day off for family, chores, meal prep, etc.