I dont know why hellbound is "cooler" or "better". for us, we know that places too much. We botted there since hellbound, so like 2 or 3 years. but GOE is a beautifull place, not so common and perfect as a farming zone (improvable size, special rooms for raidbosses).
About the difference drop: that would make our farming zone more like real l2, because differnce monsters -> difference drops is real l2 (forest of the dead, for example). But I think that it isn't a good idea for a highrate.