Well if The Witcher 3 is on your list of games you want to play you're going to want to go with Nvidia due to Physx. Here's just one of the more popular examples of how it will be implemented in that game,
Watch Dogs is also most likely going to favor Nvidia cards. If I were in your position I'd wait for the 780 ti release since price drops are most likely coming with it for Nvidia cards. If the 780 drops to $550-$600 it won't be hard to find used ones for $500 or less with life time warranties(or open box ones at micro center). To keep shadowplay simple think of it as an on the fly DVR for capturing gaming moments. To keep G-Sync simple its a new technology Nvidia developed which changes the traditional way a monitor syncs. Its said to provide a much smoother gaming experience granted you'd have to buy a gsync capable monitor once they are available.
You could drop the 250 GB SSD for a 120 GB and put the savings towards a 4770K.