P10 should have the die size around the same as 7870 <- amazing chip besting maxwells gtx960 in recent titles in both performance and performance/watt, and it is even smaller than 960.
7870 is a 120W card. Around what we expect from P10, maybe even on the downside. Even when we assume P10 will take the same amount of juice as 7870, and we apply the 2.5x efficiency on top of it we arrive at:
2.5x106%=265% right where the 980ti/tx is.
If we assume P10 is really a 150W card, as rumored, 30 additional watts is 25% more juice, at 2.5x efficiency, 1.25x2.5x106%=331% of relative performance - somewhere off the charts more than 25% faster than 980ti.
As for 7970 there will be Vega. It will probably feature 2 chips, like polaris. One would be around 350-400mmsq as a 7970 counterpart, the other will be hawaii/fiji replacement at around 500mmsq.
I think amd will focus now on small chips and perf/mmsq so they can later use with interposer in die-stacking-single-GPU Navi era as well as
profitable gaming APUs.