What is most important in dedicated physx card?

t99

Honorable
Jul 16, 2014
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I have an amd r9-270x right now and was thinking of getting a second nvidia card to run primarily for physx. What is the most important thing to look for in the card if this will be the primary use of it? I would think you would just want the fastest processor and maybe more cuda cores? Really not sure though. Would the amount of ram be irrelevant here? Would a lower card like a gt 630 even do anything?