ok, maybe this can help.
Those pelicans you are looking at seem to be 35L, right?
I don't have those bags, but ran the Hepco Becker Junior 30L hard panniers on my WeeStrom. IIRC a german mag did a test and they measured out at 28L. But here's and example of what I packed in those bags during a week long trip with camping.
Right pannier: black stuff sack--clothes; grey stuff sack--sleeping bag; chain lube; sleeping bag liner; lid--assorted head garments and shop towels.
Left Pannier: (red stuff sack--sleeping pad, brown bag --food (day use and cooking), reading material, oil, latex gloves, lid--warm weather gloves, and empty spot for the rain liners that are in-use), camp stove
the duffel bag on the back seat had the tent and the bulky heated vest, while the tank bag has the daily necessities (camel back bladder, snacks, sunscreen, kleenex, bandana etc)
is that the kind of answer you were hoping for?