Consequence selection is subject to a reasonableness test by the game table as a whole. Whatever your game table (ie. players+GM) collectively find reasonable is thus allowed as a consequence.
@Becq
By the time consequence selection is available (and thus narrative control passes to the defender), stress has already been inflicted.
For instance, that iron sword indirectly causes more stress to the Sidhe Lord who leaps off the cliff to avoid your swing than would a bronze sword because, motivated by his fear and hatred for the Bane, he leaps farther and more recklessly.