You should check out some benches of 290/970 compared to 7850/7870, it's 2x-2.25x the PS4. Keep in mind PS4 is not a 7850 nor a 7870 but something in between.
I have checked benchmarks (now and plenty of times in the past), a 970/290 is 2.5x (more in some games) the performance of a 7850.
compare
I don't see the point of claims like the ps4 gpu being between a 7870 and 7850 either, every single multiplatform game benchmark and comparison since launch has shown it to perform exactly like you expect a 7850 to perform.
Anyhow my point is that a 970 barely cuts it for 4k30 fps (and doesn't in some newer games), and that 2x a 7850 doesn't get you to 970 performance either.
They're better off going for a smooth locked 60 fps 1080p in most games than trying and failing to go for 30 fps at 40k
edit: and not related or aimed at you but I don't understand the complaints about a mid gen upgrade. It's not making the ps4 perform any worse or better than it did before and there is full backward and forward compatibility (something you usually don't get with a new console)
There's the fixed performance target argument (which was always a compelling reason to buy a console, to get that guaranteed tearing free performance), but how long has it been since developers stopped respecting the fixed performance target to actually deliver consistent performance? Most games already drop below their framerate target and/or suffer from screentearing anyhow. You can't lose something that you didn't have anymore to begin with.
I don't really see how a ps4.5 will affect any ps4 owners at all.
You still get the same gfx and performance whether a newer faster version exists or not.
edit 2: I just saw the benchmarks you added chromatic, those show that the 970 is not capable of 4k
32 average fps in mordor is not enough to get a playable framerate, you need a lot more than 32 average to not get constant dips below 30. Any ps4 game that currently runs at 30 fps locked would be running at a lot more than 32 fps average if vsync was turned off.
The 390 does better thanks to its abundance of memory bandwidth (970 has quite low memory bandwidth, even though it's still higher than ps4s), which reminds me: Surely they'll have higher bandwidth vram for their ps4k and not just use the same speed ram on the same memory bus. This info is missing from the OP