Mental stress I reserve primarily for the bad guys. It takes a lot of practice to be able to do that quickly and effectively (I.E. with evocation's speed and methods). Most good guys are not going to sit and break one mind after the next just so that they can do it flawlessly later. Otherwise I'd allow it as a ritual, or if the caster's intent is to harm the target (plenty easy to tear someone's mind up, much harder to only damage specific bits in specific ways). And of course its usually lawbreaking.
Pretty much my opinion.
But I had another idea. Not sure how it would work in game, but maybe it's something to try:
I would go so far as to say, the conflict dictates the manner of consequence someone takes (casting stress aside). So if you are in a physical conflict, you are going to do physical stress.
I know that kind of gives emotional vampires a handicap, but only slightly, I believe.
It should however be possible to change the conflict accordingly. If I remember correctly, any time an emotional vampire has been using his ability in the book, it was never mid-fight. It was either completely outside of a physical conflict, or the physical conflict ended and was replaced by a mental one (admittedly a short one mostly). I am thinking especially of Lara vs. Daddy dearest or Harry vs Corpsetaker, but there are others as well.
Ok, what am I trying to say here?
Maybe a mental attack could work similar to that. Instead of a mental attack, the mental attacker would have to do a maneuver spell to connect to the target. Once placed, it can be tagged to force the target into a will vs. will fight. Of course, both opponents would drop their dodge roll to terrible for the time, since they can no longer partake in the physical conflict. The fight itself could be resolved using conviction to dodge and discipline to attack. Or alternatively the skills that best represent the characters self image, though that seems like it should be stunts.
GS:
The fight would probably look like Molly vs. Corpsetaker.
