Originally Posted by reset smith
I've thought about the TITAN and I agree that it would probably be the better choice. Unfortunately I am strapped for cash and am not counting on any being available when I can buy one. Water cooling the rig will be even farther in the future. I've read the TITAN can be pretty damn quiet and that would be great while I save. I guess I'm more exploring my options right now and the 690 seemed like the biggest reach in terms of feasibility.
The 690 is a good choice, just be aware:
Without VSync on:
SLI isn't as smooth as a single GPU. There is small almost unnoticeable stutter when panning and moving (bear in mind a single GPU also does this, problem is exacerbated with 2 GPUS it seems). Good thing Nvidia seems to have eliminated microstutters for the most part.
VSync should get rid of just about all stutter giving you glassy smooth pans at the expense of input lag.
SLI adds 1 frame of input lag per GPU. At 120 fps it's 8 ms, which if SLI lets you get a framerate that high is kind of a fair trade off and just about unnoticeable, but 16 ms at 60 fps is a little closer to being noticeable (we can feel around 20ms of lag according to Carmack) and depending on the input lag in the rest of your system that number may push it into the noticeable range.
I was perfectly happy with the 690 until I was pointed out these things, but since I mainly play competitive twitch shooters I am considering ditching SLI altogether until Nvidia updates the tech.
But as long as you are aware of the caveats, SLI does give the biggest performance increase, allowing you to downsample, add layers of AA while maintaing 60 fps and above. And really most people will not notice the issues I've listed above.