I would turn the existing fans up for a while to see if it makes a noticeable difference.
I've found that a case side fan can make a difference providing it's spinning slowly and doesn't interfere with the rest of the airflow. Mine blows over the VRM's on my 4870 but only knocks about 5ºC off the temperature.
Not sure where PC world are coming from with their too low temps unless they mean that if it's in a really cold location you could get condensation forming as it starts up.
just how hot is your room? i don't have any central heating (yes im a caveman) got 3 msi 280 gtx o/c (650/2300) and the middle card doesnt hit 70. same case, standard fans on low, i don't think they got to your temps in the summer. your temps are well within limits im just curious why it's hotter than mine which are using the bog standard coolers. make sure you have room all around the case, and that you're reading the nvidia sensor as the ambient can be misinterpreted by some software.
i wouldn't worry too much my 8800's are still going strong after nearly 2 years old in a standard atx case the top card was never below 80c and sits mid 90's gaming, i dont think they even throttle 'till 110, might be wrong but as i said still going strong.
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