NuName,
The actual distance from the touch down point to the end of the landing run (full stop) is not effected by approach angle. The only difference is the distance from screen height to Touch down point according to the AFM figures, increase the angle...reduce the LDR. A good example of this is London City, steep approach angle and short runway. Because the standard 50 ft screen height still applies according to performance calculations this will occure closer to the touch down point therefore not 830 ft but more like 400 ft (we have almost doubled the normal 3 degree angle so half the lateral distance, not exact science). Stopping distance is unchanged.
50 ft at the threshold is meaningless, under normal approach path angles one would expect to cross the threshold approximately higher than this. Visual approaches still require a stable approach which in turn must satisfy the criteria for a stable approach. Just because we can elect to fly a visual approach does not preclude safe obsticles clearance flying. One also be careful not to alter ones Verticle speed or approach angle greatly on short final because this will trigger EGPWS warnings resulting in a go around.