I have size 12 feet and am relatively short for foot size (a tad under 5'10). My feet have often been a problem for me with rear racks and panniers...I went with a very long rack and the longest chainstays I could find.
It's funny...I got my first custom last year and my builder asked me foot size. It really changed what he did...I ended up on a larger bike than I was used to riding and he was absolutely correct, it rides better for me.