Maybe the front back difference, or lack of difference, has to do with the amount of gear we're carrying.

cyccommute, you mentioned in your first post that you notice a difference when the panniers are heavily loaded. In my case, each of my panniers carries about 12-13 lbs of gear, which really isn't that much. My panniers are also quite small, and if I mount them all the way back on my rack (and facing the correct direction), I don't have any issues with heel strike. In addition, I have a handlebar bag with about 5 lbs of gear, so it isn't like I don't have anything on the front.

The differences I did notice were:
-- I preferred to have the weight in the back on steep descents.
-- I preferred to have the weight in the front if I was walking and pushing my bicycle up a steep hill.
-- When I rode with a front rack, I struggled with hand pain.
-- When my front rack was removed, the hand pain went away. Rowan explained that one to me ... something to do with flex, I think.


Now in the case of the OP who wants to travel fast and light, he could pick up a sport-touring/audax bicycle, like I suggested, with a rear rack, and ride Randonneuring style ..... using a Carradice, like Rowan suggested, with his bivy strapped to the rack. This setup would still give him the option of getting small panniers, if he felt that the Carradice and rack weren't quite enough.