No weapons should be best for every situation, but DR-penetrating weapons should certainly be best against DR.
The problem with this is that most enemies are going to have at least 5 DR, thereby benefiting fully from the Estoc's ability. You get no more benefit from using the Estoc against someone in Plate than you do from using it against someone in Leather. Which is silly.
I'd prefer it if it was more along the lines of "penetrates 50% of DR or 5 DR, whichever is less". That way it's actually an anti-armor weapon and not an anti-everything-that-isn't-naked weapon.
I actually like this suggestion. Making the Estoc lose a little bit of accuracy like the firearms which have an accuracy penalty to offset the DR pen would maybe be something hey could throw into the mix also. That said I have spent some time using Just Ice and it isnt that bad. Sure estocs are best but I feel like people are getting just a wee bit too worked up about it.