Regarding of physX nvidia

Hello guys, recently i just bought a GTX 690. The question is should I use my old graphic card GTX 460 for the pure physX? Will it bottle neck? Or I should get a gt 640 or a gtx 650 for only physX?

 

690 is overkill already......

gtx 460 would bottleneck, maybe not with gtx 650. But either way its not really worth it,

thanks