it depends... In abyssea now elemental based WS's are all the rage. and with COR AF3 +1/+2 Feet's ability to lower the monsters resistance to an element by an argued 10%-20% i probably wouldnt be firing both my QD's one to weaken it to the WS's element and another to Magic Burst...

Unless the Burst was something spectacular or had some really good aftereffects, like doubling potency of existing debuffs of the same element as the shot...