If by PS5, you mean the console after the PS4 pro, then I'd say somewhere between 2 to 3 time more powerfull. And that's thinking it will be released in 3 years.
It sure ain't gonna be 5 times. The xbox one has to be underpowerd and flawed, and 4 years later, Scorpio is heading to be 4.5 times more powerfull.
Judging by that, the Pro isn't underpowerd, so no chance it will be that big of an increase.

What happened, they made a masterpiece in 2007, but it was too heavy for the PCs of it's time and impossible to recreate on console, so they dumbed things down for the console users and made two average games after.
Guess we can blame those weak consoles for destroying what could have been an amazing franchise.

G-sync is just way too awesome to pass.

As for 21:9 or 4k. I'd say 21:9.

4K is still a ¤¤¤{ when it comes to the necessary power to get a decent framerate, and superwide screens are just awesome.

hemmm...
1440p/100fps :S

Ok, this conversation isn't for me!!!

Well, 1440p/100fps for me... so I a mix of option 3 and 4

Well,
I tried it a few time on my 1440p monitor, but having 100+ fps made more of an impact than a higer rendering resolution.

Why, because they are great!
Seriously, they are not making a new console per year like phones, and gens are now retro/forward compatible. You don't want a new console, fine, keep the old one, just don't complain because games on more powerfull hardware look a lot better.

Instead of 1800p/30fps, I'd rather target 1200p/1440p at 60fps. I'm way too spoiled by games running constantly at over 90fps on PC now.

i7 6700k @ 4.6Ghz

Asus GTX 980TI poseidon

Msi gaming M7

Corsair Vengeance 16Gb DDR4 3000Mhz

Fractal Design Define S

Corsair AX860i

Samsung 850 Evo (500Gb)

(monitor is a Acer XB271HU, but not in the picture)

And the important part, the cooling:

XSPC Photon (pump/reservoir combo)

BlackIce GTS 420 in the top exaust.

XSPC Raystorm CPU block.

1440p/144hz/Gsync >>>>>>>>4K/60hz