Correct. RX480 has been clocked to 1450 stable and it's nowhere even near, not even same ballpark by any margin.
Just sticking GDDR5X on RX480 isn't gonna be RX 490, I'll give you that as a guarantee right now. RX480 is already well treated VRAM wise, well balanced overall, and core OC's deliver while memory OC's don't do much for most games.
Given the stream processor count I really don't see a 1070 competitor. And I also think we are forgetting an extremely important little detail: the real 1070 contender is already out and its called Fury X. AMD still wants to get rid of that stock and they go for cheap. In addition, a SMART AMD would position their high end-entry card a noticeable margin above the 1070 at a similar price point, because it will both be pushing the 1080 out of the arena and at the same time make 1070 obsolete. The 1070 and 1080 are about 25% apart in performance, if they were to position it somewhere round the middle @ stock clocks that would allow a 'OC to 1080 perf' card for a 1070 price, which is going to be a big winner in this segment, because everyone does that little OC. Matter of fact if they go down that route (wishful thinking I know, but still, it makes some sense) they may well have a '970 sales killer' on their hands. AMD has got the momentum PR-wise right now.