Having a GTX 680 myself, I advise against it. It is a great card, but it isn't worth the extra 100 bucks, unless you get a good deal on it. A GTX 670 will handle pretty much the same a GTX 680 would.
This "support" matter is of little importance. Games will run well on both if you have a decent card. Also, PhysX is pretty much useless. Very few games use it to begin with, and among those the difference of using it or not is hardly noticeable in most cases. One could argue that games such as Arkham Asylum may justify the technology, but I find that hard to support. The game is great whether or not you can use PhysX, and in fact, you will soon forget it is even there.
So, I would go for a GTX 670 or a 7970, whichever one you get a decent deal on.