marc, most folks doing walls use static lines. the solution is not to drop your bag to the end of the rope - if you are doing that you definitely shouldn't be on a wall in the first place. i prefer hauling with static lines if the bags are really heavy, but it doesn't really matter if you are hauling less than 100 pounds or so.
6mm would be madness, and 11mm is overkill. i use 10mm lines, mostly because they look stronger than 9mm lines and i find that makes a difference when you are jugging out in space way the hell off the ground. 9mm is fine too, but i tend to really beat up on ropes so i like the extra margin.
light 6mm lines are good for tag lines, which are nice to have if you are doing long pitches. i prefer using a bit thicker tag line that i could use for an oh shit emergency lead rope.
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