I would not get the 690. It has only 2GB of RAM effectively. Sure it has two sets of 2GB ram, but it acts like 2GB. That means for anything above 1920X1080 resolution you will run out of memory. IE the 2560X1600 30 inch screens or triple screens. Each new generation of games require more RAM too.
The 780 has 3GB RAM which really, in this day is far better. Of course you have the Titan with its 6GB RAM. If you had to buy now, it'd be either two 780's or two Titans. Wait until the 23rd or so and two R9 290X's will be the best. about the same as the Titan, but about $350 less per card. Then, in a month or so, we have the 780TI coming which will probably be as good or better than the R9 290X and the Titan TI is rumored, which will be better yet.
The fun never ends.