I just got my 7770 in and it has a three fan modes. 1) Single Fan Mode - just the built in fan. 2) Double Airflow - You stack the extra fan directly on top of the stock fan. The booklet for the card says it offers higher air pressure and enhances the dissipation. 3) Dual Fan Mode - There is only a small overlapping area of the fans. It claims it provides a bigger area of effect and cools the PWM module and memory on the PCB more efficiently. Which mode would you go with for the best cooling?