As Igor mentioned in a post a year or so back, each of us here at VO seem to have our own little fetish about different parts. Mine is bags. I love bags, all sorts- handle bar bags, seat bags and for the last year or so, I've been using a frame bag and loving the versatility of it.
I first used one last year on our tour of SE Iceland. I loaded the frame bag up with a water bladder and some quick snacks and lunch items. It was great to be able to reach into the "black hole" and grab some snickers bars or to throw some dinner items in there on the way from the supermarket to the camp site.
frame bags fit the same size range on both bikes.