Ive used a 31L rack pack, but I imagine the only real limitation for a larger one would be that the distance between the two end straps that we click into the tab on the panniers, might be too wide.
I've only ever seen the 70L ortliebs in a store, the plus versions. Quite impressive bags, but they can't be that common.
I'd ask ortlieb first, you should get proper info from them.