grimmjow660 :
I did some searching around and have read the R9 290 does perform better than the 780, according to Hardocp. Also how good is Physx? I hear it doesn't matter and it matters to some people
I honestly don't believe PhysX, Mantle, or Shadowplay are features compelling enough to practically affect your decision. Its all about price vs. performance.
PhysX in particular is honestly a gimmick. Games have to be designed to actually use PhysX or its meaningless, so it only works in specific ones. It can be somewhat neat, but its very rare to see it used in games in ways that are actually noticeable. Even in games that do use it, AMD users can often get the same effects, but it just leverages the CPU instead.
Mantle is similarly game-specific, though it results in some good performance increases when it is available.
bicycle_repair_man :
An R9 290 and GTX 780 are near-enough the same card, it's just that certain games will favour one over the other.
Near-enough the same card in performance, but the R9 290 can routinely be found for $100 cheaper. As of right now, no GTX 780 on Newegg is under $499, but I see many < $430 R9 290's, I even see one from Gigabyte that's $319 (!) after sale + rebate. Pretty hard to argue with getting the same performance for almost $200 cheaper.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125505