From my experience with Evo 4 and Evo7, the 4G63 engine didn't improved too much. The different body style (plus the different LSDs) makes the car handles a lot different. From EVO IX, the 4G63 engine has added MIVEC. So I guess the IX should have a noticeable difference.
However, I still love the raw power and handling of a EVO3 (a friend's car)....those were the golden days for Mitsubishi/Ralliart in WRC.