The Phenom X4 will most likely have more raw horsepower, although it does depend which model number. If you compared the Phenom X4 9950 to your Athlon II X2 @ 3.3 GHz (I know it's at 3.55 GHz), the Phenom will be noticeably faster in multi-threaded applications while the Athlon II will be faster for single or dual threaded applications.