The R9 280 sits in between the 770 and 760, closer to the 760. It pulls a very slight performance edge over the 760 (About 2 FPS on BF4). Since both are identical in price I would take the stronger card, the 280.
However, you are listing specifics that you may want to use, such as Physx. Features like that are useful to take into account. Figure out what kind of games you wish to play and see what they favor, AMD or Nvidia cards.