I would go with the Jandd rack if your going to carry over 40 lbs in your bags. Jandd has a rack that is wider and longer then Blackburn. With the longer rack you can place the bags farther back on the rack. The Blackburn will work, but I have broken three before I put the Jandd on my bike.
"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." - Arthur Conan Doyle