To follow up on what I was talking about earlier, as far as the price/performance difference between a 670 and a 680, you can find a GTX 670 for $360. A 680 can go for $460.
670 -> 680
Price increase 27%.
Performance increase 5-10%.
680 -> Titan
Price increase of 109%
Performance increase: 40%+
If you count the difference between 670 and 680 as 10%(upper end) and the difference between the 680 and the Titan at 40%(lower end, even used by someone who called it a "turd"), both examples are pretty similar. In actuality, though, the difference between the 670 and 680, even in SLI, tend to be pretty insignificant. 670 or 680 to Titan, though? Noticeable difference.
I only point this out because there are a lot of 680s in the sigs in this thread. Not to say that is a bad thing, just saying that they are popular cards, even if they aren't the absolute best bang for the buck. But would this hobby be anywhere near as fun if you only did that which was fiscally sound?
you have to keep in mind this card can do things a tesla card can and a 680/690 cant.
can not just look at this card as a gaming only card.