Crossfire 5850 Fan Issue

Hello there,

I have a crossfire setup of (2) XFX 5850 Black Edition that I have been successfully running in a HAF 932 case for the last 3 years or so. Both are clocked at 765 mhz GPU and 1125 mhz memory. This is on a X58 chipset. I always use manual fan control on both cards, particularly tuning before launching games, as I quickly found the automatic fan control unreliable.

Recently, I have experienced an issue with the primary card, when it reaches 90 degrees celcius the fan struggles to stay at the specified manual speed of the fan, regardless of the fan level specified. For example, if I set the fan speed to 100% and then card temperature reaches 90 degrees> the fan speed will fluctuate from ~53% up to 90%, but typically staying around 50%. All the while, the temperature of the card keeps rising 90 and beyond. I confirmed this happening in FurMark. This has me concerned that the card may be damaged. I have tried the following troubleshooting so far.

Uninstalled/reinstalled catalyst drivers/cc 12.10 and 12.11 beta drivers.
Swapped primary card with secondary card in different slots (they are identical). Problem still occurs with whatever card is primary.
Scaling back clock and memory slightly, first time i have ever done this. These cards are factory overclocked.

I don't understand, it's almost as if the primary card doesn't have enough power to keep the fan running at high speed while the GPU activity is high. Maybe the fan is burnt out? but that wouldn't explain the swapping of cards not working.

Both of the cards had lifetime warranties from XFX, but I don't want to RMA if I don't absolutely have to.

Any thoughts or ideas would be greatly appreciated!