Lol, I don't think you can get a GDDR5 motherboard yet, or the actual RAM, at a shop. And games aren't about having the best graphics anyway, if you can run something on low, you'll still enjoy it if it's a good game.
Oh, yeah GTX690 = 2 underclocked 680s on a single card card. That means the max you can run is 2 690s in SLI, which is reaching the 4 GPU limit of SLI.
A GTX Titan, though, is a single GPU card. 4 Titans beats 2 690s!!!!!!!!!!!!!!!!!!!!!!!
A Titan contains the most powerful GPU you can buy at the moment, just WWAAAAAAAAYYYYYYYY overpriced.
Also, GTX560 won't run Crysis 3 on max, and it'll be pushing it for BF3 even.