And comparisons on the 980/970 vs a 690?
Probably won't see too many reviews of new cards vs a 690, it was a fairly pricey card that not a ton of people bought, and its 2 generations old now. Best we can probably do is make assumptions. According to Anandtech:
680 vs 690
Metro Last Light 1600p: 36fps/60fps - 66% gain
Bioshock Infinite 1440p 53/93 - 75% gain
Battlefield 4 1440p 41/66 - 61% gain
Thief 1440p 31/56 - 80% gain
So its probably safe to say that a 690 is a 60-80% gain over a 680 in most games at the 1440-1600p resolution range
Now the stats from Maximum PC, 1600p resolution 4x MSAA on highest/ultra settings in all games
680 vs 980
Tomb Raider - 19/33 - 74% gain
Metro Last Light - 21/46 - 119% gain
Batman Arkham Origins 51/75 - 47% gain
Hitman Absolution 27/42 - 55% gain
So the 980 over a 680 is anywhere from a ~50 to 120% gain
Id say don't upgrade, assuming you are gaming at 1600p or below. Some games might actually be slightly better on a 690 than a 980. And while the top-end of the 980 might be a little higher, its just going to vary wildly from game to game. Going from a 690 to a 980 probably wouldn't be a noticeable jump in power in most situations.
If you plan on gaming at 4K anytime soon, yeah, a 980 is probably going to outperform the 690 juts due to the 4GB vs 2GB of memory, but its not like a lone 980 is going to be great at 4K regardless, you'd still need to pair up 2 of them to consistently get over 30FPS in most games.
Right now, until drivers maybe get optimized a little better for the 980, the only significant advantage it has over a 690 would be heat and power consumption. (690 can max out at 300W, 980 is almost half, at 165W)
