We use a Givi 80litre bag and I've seen two 40 litre bags fitted (his 'n' hers) which imho is the better option although we also packed a foldaway trolley which the bag hooks to and allows easier transport to and from the hotel room.
Last years photo shows the high rise on the rack which although tall & heavy proved to be totally stable on the way to & from Grindlewald. This years trip we scaled down somewhat but still managed to carry more than a travelling circus 😰
