The GTX 670 is borderline for 1040p gaming, but ok for now. In a year though you probably won't be able to max out every title and obtain decent fps. But the 4GB of VRAM do make a difference at this resolution so that's a good idea.
A GTX 680 would enable you not being forced to upgrade any time soon.
The "GTX Titan" will cost a lot more and won't be part of the new generation product-line (700 series), so availability may be very bad.