|Nvidia GTX Titan|
I features a single Kepler class GPU with 6GB of DDR5 RAM and 2,688 CUDA cores (!!!)
Pricing is expected to be around 800 pounds so it's not cheap but it only draws 250W of power so it could possibly be used in a Mac Pro (maybe in the the new Mac Pro? Hmmmmm)
Using the power of the CUDA cores with software that can take advantage of them should give excellent performance. Adobe CS6 uses CUDA for it's Mercury playback engine so this would be an great card for use in an Adobe system and Blackmagic's DaVinci Resolve would also make good use of the power of this card.
If one card is not powerful enough for you the GTX Titan can even be installed in 2 or 3 way SLI, multiplying the performance even further.
This truly is a groundbreaking card and for the moment holds the crown of the worlds most powerful GPU.
Although the price may seem high for a consumer grade card it is a lot cheaper than most workstation class cards with performance that would run rings around most of them.
I don't have the money to get one and test it but there are various sites benchmarking it in PC's.
More info from Nvidia here