Why give the number at this point? Does it really matter? The numbers may not be finalized. They're just trying to give people an impression of what it will be like, and saying it's 2x an X or 4x a One S a concept the average consumer can wrap their head around.
That's what i mean actually, i see people throwing numbers everywhere, from 8 to 16TF or even higher, but we have no information at all how many it will be. Phil only said 'twice as powerfull', and people can do what they want with that