The Radeon 9600 Pro has better overclockability level than the 9500 series due to its reduced die size (which also means lower power consumption).
With tools such as Riva Tuner, you can "softmod" the card to become the higher level cards.
To explain this, the Radeon 9500 (NP) and 9600/9600 Pro have only 4 rendering pipelines (as opposed to 8 on the 9500P/9700/9800 series); doing the softmod will supposedly unlock the 4 "hidden" pipelines to achieve the performance of the 9700.
The softmod trick will only work on the 128 MB 9500NP and up.