Is that seriously an issue? striking panneirs with your heel on bikes with a shorter chainstay? Seems like an engineering flaw that would be designed away...
I have toured ~150mi with something on my back, and that sucks. Whatever I end up with, it will be attached to my frame.
I plan on touring 80-100mi/day, camping, cooking my own food (for the most part), and carrying my own water. I am an experienced ultra-light backpacker, and I think I can get everything I need onto a rack/panneir system.
Guess I need to find a good p-clamp...