Hi,
I have the same case as you and am running a pair of GTX 570's - though both are of different design. Additionally my motherboard allows the cards to be spaced a little further apart than yours it appears - your airflow is rather compromised for the top card as I'm sure you're well aware.
I fitted a good high-flow high static pressure 140mm fan to the front of my case, mounted in the higher position. This feeds cool air to both cards reasonably well. After removing the lower drive cage I also added a 2nd (Antec 3 speed) 120mm fan at 45 degrees so it directed a little more air towards the upper card. This helped.
Tell me, do your cards vent most of their hot air out the back or into the case? Reason I ask is because my upper card vents out the back, while the lower card (different design) vents mostly into the case. Adding a cheap 120mm EXTRACTOR fan in the lower side-panel slot REALLY helped get the heat out of the case and prevented much of the extra heating the upper card was getting from the lower card.
During gaming / benching I can really feel the heat this extractor fan removes from the system, really rather a lot!
Typically my hottest (upper) GPU will not go any higher than very low 70's even under VERY heavy load from gaming (I find Crysis 2 heats things up) or Benching with something like Heaven 2.5 ... actually generally Crysis 2 is the hottest things I can do.
I'm not sure how much hotter/cooler our cards are when compared in the same scenario so maybe your cards would run equally hot in my case. However, what I've done has gotten the best temperatures I can out of my setup, so hopefully it'll be of use to you too.
Note: I did try the having the lower side-panel fan as INTAKE, blowing cool air directly onto the card - this was not as effective as taking the heat away...sorta makes sense really
Cheers,
Scoob.