HD5870 with 8800GTS for Physx

I was thinking about adding my 8800GTS to my system to use as a Physx card. Is it worth it? I have this 8800GTS in my server, which is kind of overkill. Would I see a gain in performance by having a dedicated card to handle the Physx engine in games? Do most games use a Physx engine? I seen this article where someone had the same 2 cards I do, and the average FPS was substantially higher. Is this realistic? Also, how do the drivers work together?

Here is that article: http://www.hardwarecanucks.com/forum/video-cards/31726-...

Sorry for all the questions, but I don't have much knowledge in this area.

Thanks,

Tony