AMD will have its R9 295 water-cooled cards ready soon, but we still don't know anything about AMD's pricing. We can only guess that it will be nothing close to Nvidia's.
However, the Geforce Titan Z will should be an easy sell, believe it or not. That is something that was confirmed by e-tail players, science community contacts as well as boutique PC makers such as Northwest Falcon or Maingear. Wealthy gamers will be after the card for sure, while in the science and computation community these guys believe that $2,999 is a bargain for such compute power. These guys are used to spending even more on high performance gear, so they will consider Titan Z as an affordable solution, believe it or not.
Boutique manufactures can sell their great creations for more money and it is a win situation for them. Even AIBs won’t mind the price hike as Titan Black and the original Titan were selling well at the original $999 price tag. Adding even pricier cards might earn them a bit more made cash, although the market for $2,999 cards will be very limited.
Two Titan cards or two GTX 780 Ti cards will give you probably more performance than a single Geforce Titan Z, but they will need more power. There will be people who will be buying two Titan Z cards, and imagine the power that comes out of such setup. 4K gaming with all details cranked to maximum, even 3D and maximum FSAA and anisotropic filtering should not be an issue for a single, let alone a dual Geforce Titan Z.
So this is what we expect that will happen with Geforce Titan Z. Yes, it is a pricey, niche product, but that does not mean that it does not have a market.