Well currently I have 1 rear 120mm fan (Arctic cooling PWM fan) and the stock top 120mm Tricool fan (I took out the bottom 120mm fan as my hard drive is in the upper chamber), a Shark Evercool CPU hfs and I idle at about 36º and max out at 47º while gaming.
I can't personally compare it to a 900 as I've never owned one. But it seems like the 180(2) is a lot quieter than the 900.