Originally Posted by Geriden
Not necessarily the top card is the hottest - Its the card whichever is outputting the visual to the monitor (basically which ever card i plug the DVI cable into gets hotter, regardless if its top or bottom card)
The bolded part above is interesting. Usually the 2 cards share the loading fairly equally in SLI and so the temps due to this factor alone are more or less the same. The huge temp difference usually comes from the fact one card receives poorer ventilation.
As for your setup, I imagine the top card has poorer ventilation and so to counterbalance this, my first suggestion
is to use the bottom card as the video output card.
Now, next step is to improve ventilation for this bottom card (which will have higher temp according to your observation). Your Asus Rampage II Extreme has 6 expansion slots (with 2nd + 3rd slots occupied by the dual slot GTX460 and the 4th + 5th slots by the lower card) and the 922 has 7 case slots, this means you have 2 empty bottom case slots. My second suggestion
is to install an external PCI Cooler such as Nexus WaveAir (see link below) to either one of the 2 bottom case PCI slots for air extraction. I imagine either one is fine.
If for some reason you wish to use the top card for video output, then it will be hotter of the 2 and I will then suggest you install this Nexus WaveAir to the top most empty case PCI slot.
And, the 80mm fan spins at max 1500rpm (producing 17.6dBA, not loud) when connected to a molex. However, if you have a fan controller, perhaps it is better to use it for speed adjustment in order to find the optimal fan speed for optimal card temp.
This device (~US$16?) should be more economical than buying a new case. And I suppose it will not be wasted as it can be used in any other case in the future.
Finally, as brettjv said:
But still, 90C in furmark is no big deal. If you game, and use v-sync, your probably will rarely break 84C or so, and usually be under 80C depending on the game.