The 6 GB version aka Titan Black, because that is essentially what the 780 Ti 6 GB is... lol, is due to 4K content.
Lets assume 3 GB is in most cases more than enough. But what about the time you hit the ceiling, you run into the limit and if you only had 1 GB extra it would be fine ? the GTX 880 will get 4 GB and there is a reason for this. The extra cost of a 6 GB version and considering that I will have the card for 3-4 years at least is also a dead give away why one want more than 3 GB
Nvidia just released the Titan Z which is two Titan Black on the same card which is basically 780 Ti 6 GB SLI. Price for the Titan Z will be around the $4500,- mark while the other option is roughly $1900,-.
Anyway... I am sure I will end up with an SLI config and just live with that ... lol
I thought the Titan-Z was already confirmed at $3000?
There is no way Nvidia is going to charge $4500 for a card barely better than what AMD is already offering for $1500.