Not really, better off selling them. I've tested PhysX with a GTX 780 & 750 ti on games that heavily use PhysX such as the Batman/Borderland series and it doesn't really make much of a difference. The FPS increased a small bit (about 5-7 FPS) but the temp on my 780 increased as well which caused the fans to run louder. All in all it isn't worth it IMHO.
Also for PhysX I would recommend GPU's within the same generation (or close) as that 460 may actually cause worse performance on the 970.