Alot of you guys aren't considering the scenario where the game you're playing is actually stressful enough to occupy all of your graphics power.... that's where a physx card comes in handy.
Using the physx screensaver (http://www.youtube.com/watch?v=s_2Klve_2VQ
) I get IDENTICAL frame-rates on my GTX 285 and when i have physx running on my 9800 GTX.
Now, I loaded up F@H on my GTX 285, 100% gpu utilization. I started the physx screensaver with my 285 doing the physx calculations. It's not powerful enough to handle full load from F@H and graphics and the physx.
I repeated the same thing with F@H on my GTX 285, 100% load, but had physx running on my 9800 GTX. I was capped at 60 fps during the benchmark. The 285 could handle F@H while rendering the (extremely simple) graphics. Allowing the 9800 GTX to handle all of the graphics work.
You guys with the 480's in SLI. Try and run metro 2033 at 2560x1600 with AA / AF, benchmark it, then run the same thing again with a dedicated physx card. I can guarantee that you'll see the benefit of a physx card when your graphics solution starts to hit a wall.
... granted I don't know if the 480's will even choke with metro 2033 at that res, but people saying they see no improvement are looking at the wrong facts because no matter how you try and slice it, ever, you'll see a benefit from physx. Whether it's worth
the heat / power is another story
@ Eltigre88 - It's because he's limited by the physx card.... it's too "weak" to power physx at a rate where it keeps up with how fast (in the best case, no graphical load) a faster gpu can do it.... You have to realize a physx card just normalizes the work load by spreading it out among 2 gpus (by 'it' I mean the tasks required, physx and graphics). It will raise the mins and certainly can lower the max's too if the physx card can't process physx only time-frames as fast as the main card.
- The only time you'd never see this happen is when you're using 2 GTX 480's for example (not in SLI). The Max should never be lower when using phsyx on a dedicated card (when the 2 cards are matching). UNLESS your motherboard drops to an 8x pci-e slot then it's possible to see a lower max.... currently i'm running 8x/8x for my GTX 285 / 9800 GTX setup and I haven't seen any negative impact because of it.
It's all just math... stop and think about it and it'll make sense