Right now i have a nvidia geforce gtx 670 in my computer. it does run everything amazing.
I just want to know that if i were to add a gtx 650 ti for SLI in games like arma 2 and skyrim or as a dedicated physx card for in games that support physx (borderlands 2) would it improve gaming graphics and fps, or would it make it worse.
You can't SLI a 670 with a 650 ti, only another 670... And adding a 650 Ti for physx will improve your FPS in the games that support it but not enough to justify buying a 650 ti. If you want to improve your performance in all games i would suggest just buying a second 670. On that note what is your PSU/system specs?
Well that would be enough to run 670's in SLI, Is that what you plan to do then? IMO the 650 ti would be a waste of money.
Does your motherboard support SLI? And what is your CPU? No reason to go SLI if your cpu will hold you back anyway.
If you want to run PhysX, then get a low end second card just for PhysX -- not SLI tough.
PhysX does not need a high end card, so get a second hand 8800 GT at eBay, wherever, then set it just for PhysX.
That's a common misconception... You DO need a medium end card for PhysX otherwise it's going to negatively impact your performance... a 8800 gt isn't enough but a 650ti would be enough. (if you go high end, might as well as just set it to SLI instead of dedicated PhysX since it won't fully utilize the gpu)
The current way that PhysX is set-up, when you assign a GPU to PhysX, that card is the ONLY card that will do PhysX work. If the card is too slow, then it would slow down the more powerful GPU doing the rendering...