Off the mark you'd feel like adding a GTX 465 as a PhysX card is waste of time, power and money. When you start getting stuck into some real world games, though, like Batman AA and Dark Void, you can see that the inclusion of the card really begins to show some serious potential.
It's really worth noting that as we see more and more games that support PhysX and the technology becomes even more intensive, a good quality NVIDIA card used alongside your current one as a PhysX card is going to really be put to good use.
PhysX isn't at that level where you have to have it; we're not sure it's ever going to get there for the simple reason it's a side technology, in much the same way Tri Monitor Gaming and 3D is. What we hope for, though, is that more and more companies make use of the technology.
Today you can see that palming off PhysX to the CPU just isn't an option and brings games to a crawl. And looking at the results, a dedicated PhysX card to even the mighty powerful GTX 480 finds that we're moving from a non playable experience (Batman AA: 2560 x 1600, PhysX High, Minimum 22 FPS) to a playable experience (Batman AA: 2560 x 1600, PhysX High, Minimum 33 FPS) and this is exactly what you want to see.
PhysX on a whole is quite an exciting technology and we're glad NVIDIA are concentrating on trying to get game companies to make use of it. At the end of it all, anything that makes our overall gaming experience better is appreciated.
We're not so sure if you're on a GTX 480 you should rush out today and buy a GTX 465 as a PhysX card, but in saying that we would throw it on the 'to do list' when some funds become available; especially if you're a high res gamer.