I cant really think of a good reason why they wouldn't let reviews out now if it's that good, either.If it's true that it OCs so well to be comparable to a stock 1070 I'd be baffled as to why they haven't shown that off yet.
That would surely be a HUGE shakeup in the GPU market if a £200something AMD card compete with a £400+ 1070
Only thing I can think of is that they want to let Nvidia sell enough 1070's that they would find it hard to immediately price drop in fear of upsetting all those customers, but I dont think that'd stop Nvidia and there's precedent for doing it, too.
Just doesn't seem to outweigh the positivity they'd get right now while also converting plenty of those potential 1070 sales into 480 sales.
So yea, I dont get it.
I suppose it may be possible that AMD have authorized a few controlled leaks, though....