If you get one of the many custom factory overclocked GTX 780's, your performance level will be right at that of the Titan. Of course, the GTX 690 will still be "faster".
The 780 is 10% slower that the 690 but only uses 1 GPU, easily made up by overclocking (690's don't really overclock at all) and the Titan is a 780 with a different name.
If you get one of the many custom factory overclocked GTX 780's, your performance level will be right at that of the Titan. Of course, the GTX 690 will still be "faster".