Ultegra BR 6800's; Increase the reach to 53mm-54mm? Can Ultegra BR 6800's pad-reach be increased to say, 53-54mm by filing the arm slot longer with a round file? Is there enough aluminum to do this without getting too close to the end of the end of the slot?
I increased the reach of my front 6800 by about 1 mm with a Dremel tool because the tops of the pads were extremely close to the tire mounted on my dynamo-hub rim when the front light was mounted. I don't recommend modifying the brakes in this way. No doubt it will void any warranty. I didn't have time to replace the brake with one with a longer reach before I left for a bike trip. I've ridden more than 2500k since the change and don't notice any difference in function. However, I believe my 1 mm modification was about 1/3 of what you're suggesting.