to be honest one gtx690 is not going to have enough cram to run most games on max settings. I would either invest in two gtx 670 4gb SC cards or even two GTX 680 4GB FTW cards. THe FTW cards blow away the gtx 690 sli'd and is around the same price point.
Here I need to show you something...
I took some pics of me playing skyrim last night...look at my Vram usage
On low areas without a ton of pressure it is using at least 3gb of Vram on EACH card.
In higher areas its using almost 3.8gb of Vram on each card.
If you are spending all that money on a gtx 690 and it only has 2gb of vram dedicated for each port, you will never have enough Vram to run games at max settings triple screen. I am almost using the full 8gb of Vram. To be precise i'm using 7.6gb of vram.