The problem is where in NV's roadmap and that recent public statement a performance increase would be an "up to" figure and where "average".
Roadmaps are funny things. You sneeze at them and they change.
The older roadmaps showed a 5x times difference (SoC level/theoretical maximum) between T3 and T2 and a 2x times difference between T4 and T3. It hardly can be that it's an "up to" figure in the first case and an "average" for the second.
Either NV is just firing around smoke to surprise its competition or the performance increase for Wayne is way more humble than many of us expected.
Or, marketing just likes to throw numbers around....
From what I recall the 5x times for T3 was:
2*A9@1GHz vs. 4*A9@1.5GHz = 2.5x
8 GPU ALU lanes@333MHz vs. 12 GPU ALU lanes@520MHz = 2+x
and the remaining to reach the 5x probably for the 5th CPU companion core
The point isn't how realistic any of the above is; we all know how marketing works in that regard and those funky up to 5x or more times are nearly everywhere to be found and not just at NV. What raises a question mark is that 2x times SoC performance claim for T4 vs. T3 if it should follow the same reasoning. As I said either a nasty trick to fool everyone and it's an average increase or it's merely a shrinked T3 at higher frequencies. I still consider the latter scenario unlikely, but the question mark remains with that kind of vague marketing parlance.
Given the marketing emphasis on core count, I'd say remaining quad-core has a lot to do with how conservative the numbers are this time.