The 9600 pro is significantly faster than the 9600 ? probably about 25-35%. The memory on the 9600 is clocked quite slow, only 200mhz (-4ns) and it?s quite a bottleneck to the 9600?s performance.
See ...
nordichardware
9600pro 400/300
9600 ? 325/200
I'm not sure how much that ?4ns memory will overclock, it?s going to depend on the manufacturer and how good the ?4ns memory they use is. The core of the 9600 (325mhz) should probably make 500mhz without much problem which is well past the 400mhz stock clock of the 9600 pro, but that?s not going to help performance a lot without faster memory.
If they are pretty close in price I would have to say go for the pro, the memory is 50% faster.