Have an airflow question if anyone cares to input. Just switched back to an all-air build. I'd like to keep things as quiet as possible and maintain positive air pressure, while shaving off a few degrees on the GPU under load. Right now my fan setup is pretty minimal, intentionally, and giving me surprisingly good results:
 
2x AF140L front intake
1x AF140L rear exhaust
NH-U14S cooler (with 1x NF-A15 140mm fan) push setup toward rear exhaust
 
I've removed both HDD cages at the front of the case, so there is nice empty space between my GPU and the two 140mm intake fans. The top cover is currently on the case, so it's closed completely at the top. I'd like to shave off a few more degrees on the GPU under load if possible. In case my sig doesn't show, this concerns Corsair 760T case w/ 1080 Classified. 
 
Will adding another AF140L fan at the bottom of the case as intake make that big of a difference? Would doing this require another exhaust fan to help move all the air? Thank you.