Apples with oranges lol.
980gtx vs two top cards from the previous generation. 8800gtx vs two top cards (albeit in one package) from the previous generation. If you object to using 780s, use the titan then, its two years old after all. So, how does the 980gtx compare to two titans?
If you want to talk apples and apples then start doing so. My point was the 8800gtx was as fast as any two cards (single gpu) from the previous generation. The 980gtx isn't. Not compared to two 780tis, two 780s, two 290x's. Not even close. Still its a fantastic gpu, really is, but you are living in a fantasy dream if you think the gap is anything like it was with the 8800gtx.
I answered this in the post you quoted, but to expand, the issue with the 780's and Titan's is that they are unique in card progression and so cause issues comparing them to previous cards, however the is a simple solution.
Either you consider the 780's/Titan's (and the R290's their existence created) to be a tier of super cards which hasn't existed previously (or since, no new titan/780, yet) as Nvidia intended. Or you consider them the high end cards and the GTX670/680 the mid range (making the GTX580 the previous flagship), you have to choose one of these methods as any attempt at comparison while trying to consider the 680 and 780 both as high end generation flagships simply fails as comically as the idea that they are.
If you take the first method: then you simply ignore them for purpose of an apples to apples comparison, making the 980/690 comparison the same as the 8800GTX/7950GX2 comparison (which they are for all intents and purposes, this is the best way of comparing it) and showing the GTX980 to be every bit as good as the equally priced (accounting for inflation) 8800GTX.
If you on the other hand take option two: then it becomes a bit more complicated but still doable, the thing you have to factor in though is that from a performance standpoint the GTX780 IS the 8800GTX, the GTX680 (being midrange in this comparison) would be the 8600 and the GTX580 (being the previous flagship) would be the 7900/7950 (call the GTX590 the 7950GX2, that works too), the GTX980 would in this comparison be the GTX280, in which case the 980 costs less than the 280 BEFORE inflation, and the 980 beats the 780 by ~ as much as the 280 beat the 8800.
It's long winded (I did say the first method worked better) but the only way of getting a proper apples to apples comparison due to the way Nvidia messed around with the 600/700 series in the same generation.