Dark knights utilized coppor quad heat sinks, right?
Heat sinks just dissipate heat better. It's still going to hit your top card. That's why the Cyclone was good, because it got the air off of the cards. You're quite right in assuming it was the air circulation.
I just find a single card easier to deal with. That is why I suggested a 5970. Plus you can OC it like a wild banshee (well not really OC, just bring the clocks back up to the 5870 clocks or more)