I use 12x12 layouts against a 1 page PL page, like here:
I also split up the 4 6x6 pages into different layouts:
Here I cut up a 12x12 layout into 4 6x6 squares:
Here I cut the 4 6x6 protector in half and used it as an insert with 2 6x6 layouts (resized from 12x12) on each side:
I also do 8.5x11 layout inserts: