The 690 killed the Titan over 1 year ago. The 6GB of ram on the Titan is a con as the core clocks as well as the TDP are so low on the Titan that the 6GB will never be used while maintaining a constant 60fps or even higher so wether it has 6GB or 60GB its irrelevant and pointless. 3GB is the sweet spot for core-amount of memory ratio while providing good performance without a bottleneck.
When using Titans in 3 and 4 way SLI the 6gb of vram does come in useful @1600p playing Crysis 3 they use 3.5gbs @higher resolutions even more.
Look out for a 790 consisting of either 2x770's or 2x780's. Keplar Technology and cooling allows for the possibility of 2x780's.
They have already done it a year ago, complete with one of those Titan type coolers - the GTX 690 (two gk104 chips with better memory than the GTX 680). You will not be seeing 2x780s on the same card anytime soon either unless NVidia want to give it a TDP of nearly 500 watts lol.
