Shouldn't you take esram into account since they switched to GDDR5?Scorpio at 6TF is about 4x the performance of XB1. 4K is 4x the pixels of 1080p - that's all your extra power gone in an instant just for the higher resolution. 60fps would be another 2x which simply isn't available.
I hope they'll resist trying to play one-upmanship and have 'native 4k' purely as a bulletpointl I'd rather they use a form of reconstruction to get a high quality 4k output without using up all the extra performance, and then increase other aspects like lighting, shadows, world detail etc.