So an hypothetical PS5 in a couple of years is going to be in the GTX 1080 range? 1080 Ti?
Count on 8 to 10 tflops GPU wise from AMD(my guess is around 10.X) . Remember this thing will have to fit into a semicustom APU for 399 atleast and will also house Zen architecture and likely HBM 16GB...that should be enough at 10 or 7nm.
The GPU jump will be good compared to PS4, but its the CPU and bandwidth upgrades which are the real stars.
You can also expect sub 4K games on PS5 as well along with 30fps, devs will want that power as much as they can to push.