At least on full load, the side and rear front coolers will still run at lowest speed and maybe will keep this card cool enough instead of his own cooler and "take off" when the fan is in full load.
PS: For the 6850 SCS3 with a 80mm fan, lowest RPM given by MB and open case, 30C ambient it hardly gets over 60C on full load. The fan is put with rubber pins at the bottom of the case and in a midiATX case (i think) the distance isn't very big between card and fan. This distance is better for low temps then the attached version of same cooler as i noticed. And with a 12mm fan on low RPM put in front and side its a bit cooler too.