I made my own liners and have 2.5x8 c&c cage. I use two 2.5x4 c&c size liners. They are quite large, mine are made with wadding and so the bonus is that whilst they are large they are light and dry super fast.
Depending on what yours will be made with I think that will help decide. Having smaller liners isn’t a bad thing as they will be easier to brush hay and fur off, wash and then switch if one is more dirty?
I use a lot of smaller liners in the cage in high traffic areas, so my big liners only need washing once a week on cage clean day.