I have an AMD 7970 Vapor-X, and due to a fans being too loud and one of them turning on only after pushed to over 75% RPM, i would like to make a fan mod.

Idea 1) I would remove the plastic chassis, and add two currently unused 120mm case fans, which would be suspended from the GPU using zipties, blowing cool air towards GPU. Some guy actually already did it.. I would probably have to buy a fan controller to connect and control those fans.

Idea 2) I would buy one 140mm 4pin PWM Fan and do the same as above, except i would connect it to the GPU, which would allow regulating it depending on GPU temperature. I would use this fan on my case in the future, after eventually buying another GPU. I could also have another 120mm 3 pin fan at a constant RPM alongside 140mm fan with scaled RPM.

My biggest concern is how would a 140mm PWM fan scale with the GPU software. Would it be too weak, or too loud? I would appreciate any input on this ghetto idea from the tech savvy. Please note that silence is more important than performance to me, and if i spend any money on this it would prefferably be on components i could also use in the future.