I have a 6850 mounted onto a micro atx board. the card is already blocking one PCI slot and extremely close to the other one. I want to install an internal wireless adapter but I'm not sure if it will be too close or not... when it's installed it will be millimeters away from the fan ( might even touch the shroud)
So there is a bit of a myth going on here. The amount of air that will be moved by your fan will not change that much. However the air flow will change. You will have a decreased airflow around the center of the fan where air is not very accessible and an increased air flow around the outsides of the fan where air is easily available.
Basically if the fan is spinning at the same speed you are still moving the same amount of air. But since you are pulling the same amount of air through a smaller opening the fan will be working harder and there will more noise from the increased airflow around the outsides.
Si went ahead and installed it because i'd already bought it. sorry for bad image quality. does this look okay? it only goes about halfway up the fan and there's about half a centimeter of space between it and the fan.