Like you said, that distance will depend on individual skill, but a dot will carry you further, fast than irons.
Whether that distance is relevant to a self defense situation is another question. You mentioned elsewhere that the majority of CCW firearm use is inside 7 yards; if that is your assumption to base the remainder of your analysis on, then a dot probably isn't worth the money or time.
If we change that assumption, and 15-25 yard shooting is on the table, a dot starts to become much more valuable. The same thing applies to shooting on the move, dots have an advantage.