you do NOT have a freaking clue what you are talking about. hardware physx is done on the gpu and if your main gpu is fast enough then it can handle the graphics and physx just as well if not better than offloading to another gpu..
Running PhysX on your primary GPU only makes sense when that GPU isn't being fully taxed and has unused resources.
that means the faster your main gpu is then the faster your physx card needs to be or you might as well let the main card do everything
I don't know how you draw this conclusion, because as I've repeatedly told you, PhysX is set at the
SOFTWARE level, and not the hardware. Having a fast main GPU doesn't necessarily mean you need a fast PhysX card. The PhysX card only needs to be fast enough to handle the PhysX workload so as to not slow down the game.
If your primary GPU can't do both rendering and PhysX at the same time, you can lower the number of particles by adjusting the setting. Same if you're running a dedicated card.
an example is that a Titan can run graphics and physx better than offloading to a gts250 and that is a fact.
No it's
NOT a fact. If the Titan is being taxed by having to render the game at a very high resolution and 3D settings, then adding PhysX to the mix will degrade performance. For example, if you're running Metro Last Light at 2560x1600 with SSAAx4 enabled, everything on very high... What then?
Suddenly the Titan is out of enough resources to run PhysX. That's when you put a dedicated PhysX card in there, and even a lowly GTX 460 which is far slower than a Titan will boost performance considerably because it can easily handle the PhysX in Metro last Light.
now if you have a gtx470 or gtx480 or then sure the gts250 for physx will help as its better than a gtx480 doing both graphics and physx.
It doesn't matter if your primary GPU is a 480, 680 or a Titan. What matters is if it's being fully taxed, then even a GTS 250 can ease the burden by offloading PhysX calculations.
Your graph proves this in fact.
that is why there is no such thing a physx card being made anymore. heck Nvidia does not even tell you what cards to use because it will always change based on how demanding the game is what your main gpu is.
People that run dedicated PhysX cards like myself, typically play at GPU limited settings. If you don't play at GPU limited settings, then getting a dedicated PhysX card doesn't make sense.
EDIT: maybe a picture can help you understand. an 8600gt would help or break even with a gtx260. I know because I used that setup and there were reviews of that too. but as you can see its too slow if you are using a gtx480. well that gt240 that is barely helping the gtx480 would only slow down gtx680 and goes on and on. so again the faster your main gpu is then the faster your physx card has to be.
If anything, that graph helps my argument because it shows how running even a lowly GT 240 with only 96 shader cores boosted performance over running PhysX on the 480, a much faster card and did not slow it down.
Also, a 9800 GTX is slower than a GTS 250, which is the PhysX card I used to play Mafia 2 and it still delivers very playable framerates. And once you get to a GTX 275 and above, the performance gains start to level off, because the PhysX workload is completely handled with ease.