I has a pair of the Jandd large mountain panniers with a Blackburn XR-1 rack. The problem I have run into is that the panneir has gotten caught in the wheel twice now, once on each side. It seems there is not enough support for the bottom corner farthest back. It can move around a bit. When I'm stopped and just push on it there is ~3in from the pannier and the wheel so I'm not completely sure how it is able to move so far in to get stuck in the wheel.
Both times it has happened it tore a 3in hole in the pannier so I would really like to keep it from happening.
Was thinking of getting a rack that had a little better support farther back like Blackburn TRX-1 or EX-2. Maybe the Axiom Streamliner DLX. Would consider a surly rack but they are a bit pricey.