I am not sure what 120 x 2 you are talking about... I can tell you that if you are talking about the Swiftech then you are going to be needing Kaze Ultra 3000 fans or at the very least you will be needing Yate Loon high speed 120's
I agree, more rad is allways better but if not looking for bragging rights temps or very quiet operation and you push enough air through it, it is absolutely astounding how much heat even a single 120 (not recommeded at all in your application due to the 100% load dual cards) will dissipate. With what you are doing I would recommend doing whatever it took to get as much rad as you can.