I've got 8x20 and 14x17 Chamonix cameras coming in the next few weeks and even though I've sussed out what I like for *8x20, I'm having a hard time deciding on a pleasing mat size for 14x17. I tend to like a fair bit of breathing space but none of my mock-ups look right so far. Those of you that shoot 14x17, what do you use? Thanks!!

*I've decided on 15x28 for 8x20