Or maybe the 240 is quite a bit slower for Physx than 9800GT? What's a 240 anyway? I'm not up to date with NV's lower end offerings.
Still, in my experiences GPU speed matters little when talking about dedicated Physx cards. All that matters is that you have one that is solely used for Physx.
That's why I'm surprised that a 480 + 240 can only manage: