Your GPU fans are sucking the air in, not pushing it out downward. The air shoots through the heatsink and out the side and top of the card. Hopefully your case exhaust fans are capable of dealing with the extra heat.
Here's some basic info on Turbo Boost 2.0:
GTX 700 series cards have a setting called "Temp Limit". This is a pre-defined temperature setting that the card targets and tries to maintain. On a GTX 780, the Temp Limit is 80C (no surprise you're running at exactly that temperature!). This is NOT the same as the thermal threshold, 95C, the point at which your GPU can suffer damage.
http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-780/specifications
The video card will increase its Turbo Boost clocks as long as...