both of them aren't worth it IMHO
you should be ok with the V6GT at this moment. If your seeing bad temps with your current cooler, maybe you haven't mounted it properly or there is an issue with your cases airflow.
Airflow - You can improve on these by using another TIM, doing cablemanagement or actually getting another case. However, the last point is useless, as you have a NZXT Phantom, amazing case for stuff
How about venturing into real watercooling territory? for $200