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You can run Physx of the CPU on low, high is nvidia exclusive. But IMO it looks totally overdone and unrealistic (too much bling!) so I don't use it.
Shadowplay is important if you want to start a letsplay career as xx[random name]xxHD and do lots of screen capturing with minimal fps drop. (Radeonpro dev announced a similar feature for the upcoming 2.0 version)
No doubt the 760 is the stronger card, but as its over your budget you may have to consider if its worth the additional gaming power (gtx suck for compute) better save some cash and get the 270x