Well, the GTX 980 is launching at $550 and the GTX 970 launching at $330. And assuming the leaked benches are accurate (Can't find anything to disagree with those yet) The 970 is somewhere between the GTX 780 and GTX 780 Ti in terms of performance. Currently I have an HD 7950 and a Corsair TX650. I assume the 650w power supply should be enough consider I was able to run 7950 cfx for a short time on it, plus the fact that the TDP for the 980/970 is 165w.
So what do you guys think of upgrading to 970 SLI? Think it's worthwhile? Or would it be better to get a single 980, a single 970, or wait for more cards (such as a 980 Ti or the 390x)?
In my opinion one more powerful card is better than two less powerful cards.
As for wattage, 650W should be more than plenty. I ran an HD6950 and a GTX770 for Folding at the same time for a few days on a 650W power supply and nothing broke (I wouldn't recommend it though since the power supply got pretty toasty).
Not necessarily, not when taking price into consideration, for instance at $550 for the 980 and $325 for the 970, you could get two 970s for almost the same price as a single 980. The 980 has a big price premium, chances are the most demanding games, the games which need it the most, and at high resolutions, they will scale well, near double.