Well let me rephrase my question:
Since Arreat Summit says that Physical resistance is capped at 50%, THEN the skills calculator is wrong, because it showed a +80% to physical resistance, which it should not have.
I'm asking because I would like to know if its worthwhile to dump all points into Fade (and get 30-40 Fade). If it's linear increase, I would do it. If it's diminishing returns, I will not.
Physical resistance is capped at 50%. However, if someone were to cast amplify damage on you which is -100%. You would have -50% physical resistance left. In your case, if you have 80% physical resistance, and someone casted amplify damage on you, you would have -20% physical resistance left.