EVGA G3 or G5 Gold 850W are good options that fit.  
I picked up an Aurora R8 with the 450 W power supply. I am getting back into 3D modelling and want to upgrade my video card. To do this I need a bit more horsepower out of the PSU. Looking at 750 or 850 w unit. Just wanted to reach out and see if anyone else has done this and if there an anything I need to watch out for with respect to fit etc. (or any recommendations)  Am I wrong in assuming that an ATX power supply would fit  Thanks Lil  
Aurora R8, PSU upgrade