Paterson made a device that took paper up to 5x4 to make test strips. It had 5 'fingers' which could be used to block off light to the piece of paper being used. I normally use Kentmere fibre for my better prints and buy a 12x16 box because this works out cheapest. However to avoid cutting down a big sheet I also have a box of 5x7 which I either cut into 2 or 3 pieces and use that. I very rarely use more than a complete sheet of 5x7 to make a decent 12x16.