For applications that require the Titan Z's wicked amount of double precision floating point performance (2316 Gigaflops versus the R9 295x2's 1408 Gigaflops) that's where the Titan Z would excel over the R9 295x2. Make no mistake, because of the GeForce GTX branding, the Titan Z is a GAMING GPU, not a workstation GPU. If it were a workstation GPU it would be part of their Quadro line.
Here's some statistics about each card that I assembled:
Nvidia GeForce GTX Titan Z:
Stream Processors: 2x2880
Texture Units: 2x240
ROPs: 2x48
Core Clock: 706 MHz
Boost Clock: 876 MHz
Memory Clock: 7GHz GDDR5
Memory Bus Width: 2x384 bit
VRAM: 2x6GB
FP64: 1/3 FP32 Floating Point Performance: Singe Precision: 8150 Gigaflops. Double Precision: 2316 Gigaflops
TDP: 375W
Width: Triple Slot
Transistor Count: 2x7.1B
Manufacturing Process: TSMC 28nm
Launch Date: 05/28/14
Launch Price: $2999
AMD Radeon R9 295x2
Stream Processors: 2x2816
Texture Units: 2x176
ROPs: 2x64
Core Clock: Unknown (rumored to be 892 MHz)
Boost Clock: 1018 MHz
Memory Clock: 5GHz GDDR5
Memory Bus Width: 2x512 bit
VRAM: 2x4GB
FP64: 1/8 FP64 Floating Point Performance: Single Precision: 11264 Gigaflops. Double Precision: 1408 Gigaflops.
TDP: 500W
Width: Triple Slot
Transistor Count: 2x6.2B
Manufacturing Process: TSMC 28nm
Launch Date: 4/21/2014
Launch Price: $1499
In conclusion, with the gaming performance that I've seen on both cards on YouTube and judging by the numbers above. I believe that the Titan Z is a low power way of having a high compute performance and gaming performance card.
The Titan Z would be ideal for somebody who does graphical and special effects work, but also is a video game enthusiast, and doesn't want to get a massive power supply to support 2 x R9 295x2's or 4 x GTX 780 Ti's. In my honest opinion, if you're a hard core gamer, for the price, I would look into either getting two 780 Ti's SLI'd or a single R9 295x2. I won't try to sugar coat it any longer... for the price... the R9 295x2 kicks the Titan Z's ass when it comes to gaming, it is a pure bred gaming GPU. The interesting thing is that the R9 295x2 has a MUCH higher single precision performance, which is strange. For half the price, it does everything almost as well (90% the performance as the Titan Z).
The R9 295x2 is an amazing card, and I'm very unbiased. I have owned a myriad of AMD and Nvidia GPU's. The only downside to the R9 295x2 is the TPD of the card. The 500 Watt TPD requirement is quite high. You can't beat an integrated closed circuit water cooler though. In terms of price/performance ratio, the Titan Z gets slayed pretty hard by AMD's R9 295x2. I'm currently not seeing a market for the Titan Z besides people with money coming out of their ears who want an in between of both worlds. A graphic designer, or somebody running servers would go with Nvidia's Quadro series, or AMD's Firepro series. An enthusiast gamer would go for dual GTX 780 Ti's or the AMD R9 295x2. In short, the R9 295x2 is not better than the Titan Z at a 3000 dollar price point, but since the sticker price is 1499, then the R9 295x2 slays it