What I'm planning to do with one of my systems (it's been in the planning stage for some time, despite having all the bits) is have one rad where the fans are controlled via PWM by the CPU and one where the fans are controlled, via PWM, by the 1st graphics card. Both will use a splitter with Molex connection to actually power the fans, just want the speed control done by hardware.
That way it can be dynamic. Fans really low when idle and then ramp up when gaming, much like with the air coolers, but hopefully not as much.
My GTs are controlled via PWM