I would keep expectations in check. It will be by far the fastest single-GPU card out there, but won't trump 690 or 7970 in crossfire in gaming performance.
here's what Tom's Hardware says (without revealing numbers):
Pay the same $1,000 for a GeForce GTX 690 if you only want one dual-slot card and your case accommodates the long board. It remains the fastest graphics solution we’ve ever tested, so there's no real reason not to favor it over Titan.
The Titan isn’t worth $600 more than a Radeon HD 7970 GHz Edition. Two of AMD’s cards are going to be faster and cost less. Of course, they’re also distractingly loud when you hit them with a demanding load. Make sure you have room for two dual-slot cards with one vacant space between them. Typically, I frown on such inelegance, but more speed for $200 less could be worth the trade-off in a roomy case.