Just to let ya know the 01 RS center diff is different than the WRX diff. The RS diff is a 1:1 ratio which allows the RS to run 4.11 front r&p and a rear 4.11 ratio. The WRX is a 1:1.1 ratio that allows the WRX to run a 3.54 rear diff ratio with the 3.90 front r&p. So if you went with the RS center you would have to get a 3.90 rear diff. Just a little clarification.

Josh