no sense in spending that much money on a gtx 260 when I do believe they recommended a 9600GT for good/smooth Physx effects.
Considering how few games there are with PhysX, buying a decidated card is a dubious choice. However, if you are going to get one, know that a 9600GT gives poor results in the only game I used it with, Sacred 2. A 9800GT was almost good enough for smooth results all the time.
I believe the 250 is usually the minimum requirement for perfectly smooth play with physX. That is, unless you play Dark Void, which needs a 260.