I run a 03 WRX with the 5x100. and ran the Cusco 2 wayMZ. Loved the diff. Unfortunately, I have tore ring and pinion teeth out of 2 R160's since last Oct at VIR. 430 WHP, 18 PSI.
Bought a stock R180. I had DSS axles in the car, called them and told them I was upgrading to the R180, and they "hybrided" (if that's a word) my axles to the R180, and keep all my existing hubs, brakes, ect.
I talked to Lee, and it was a $500 upgrade. I have too much invested in the 5x100 setup and will stick with it.
I do hate te factory rear diff and will be getting another aftermarket.
Posted for relation of axle possibilities.