I'm currently running two sapphire 6950 in crossfire and playing bf3 the outside card gets around 62c but the inside one gets over 73c. Between the two card there is just an slot gap and I'm wondering if installing an stright pcie riser that rises the card 2cm (0,8") will improve significantly the cooling? Does anybody have simmilar experiences?
I would not suggest using a PCIe riser if such one exists. It could possibly cause more problems by giving more resistance (electrical) to your video card.
What is your case? You might want to look into getting more case fans/ bigger ones if your case supports it.
Also do you have your case fans with a proper push/pull system? For example - say you have 2 fans in the front for intaking air, and 2 fans in the back for expelling air - that's somewhat of a proper push/pull system.