Titan lack is for people doing 3d rendering work n stuff not for gaming :S Definitely don't get 2 780ti's thats like wanting to kill a sheep and dropping 100 nukes on it, complete overkill. I would advise you to just wait or if you really must get something 1 780 would be fine
edit: wait I just read this right, you have a 690 not a 580, need to learn how to read again. Ok why the (restrained expletives) would you need to upgrade from a 690 at this point in time, that card is still pretty insane.