The GTX 670 is a great upgrade over your GTX 560 Ti. It's even faster than 2 in SLI, I came from a GTX 560 Ti SLI and upgraded to a EVGA GTX 670 FTW. The card is only $400 and is faster than even a reference GTX 680 in most games while costing $100 less. You can always get another one later on to SLI and it will be a beast for a good while. I can max out BF3 on ultra with constant 60+ FPS with VSYNC on at 1080p.
The GTX 7XX won't be out for a good while, I speculate that those cards won't be coming out until around next Spring.
The GTX 670 uses as much power as your GTX 560 Ti while being over twice as fast, it's an amazing card and you will not be disappointed.
Go with the EVGA GTX 670 FTW, it's cheaper than the ASUS GTX 670 DC II TOP and it's just as fast while being a few degrees warmer at full load. Both the ASUS and EVGA FTW are even faster than reference GTX 680's out the box.
I advise against paying $400 for a new gpu when you already have 40-60 fps in most games. More than 60fps isn't noticeable anyway due to the 60hz max refresh rate of most monitors so don't waste your money.
Care to elaborate? What model was it? Do you have the GTX 670 FTW? I have it and talk from experience with it. It's been a fantastic card. EVGA has hands down the best customer service and have had not heard of any GTX 670 FTW cards bursting into flames.
The ideal thing would be to change your graphics card every two years, the 560 Ti is still a capable card, so you shouldn't have any problems by keeping it a year and a half more and change it with a 760 Ti.