An open air setup with the 1 card plugged directly in the first slot and the rest of the cards on extenders and arranged in staggered position (@ 130 - 140 degree angle) is about 10 degrees cooler than any closed case setup I've used in the past.
If I had more time and/or was more enterprising I would design the 180 degree (angle not temp
) setup that's in my mind. Basically each card installed flat on platform above MB and fans blowing to the sky... I never understood the card separated by clothespins or blowing hot air into to each other setup. Except for space limitations I suppose in huge setups.