Rx570 sapfire vs gtx1070 on old pci exp x16 v1 mothers with further hardware upgrade?

Question

Video cards

Does it make sense on a cheap gaming PC to chase the shader version? 5 or 6!
or chase fps in 4k? 20-60!
for a phased long-term update
, is crossfire much more flexible than slide?
for example, take a radeon 570 and then more abruptly vidyuhu 590 and pair it up?
just on the old motherboards of the version - 1 derjit 150 watts !?
and radeon 570ya is the only one for 8gb within the power of 150 watts?
and even 4k+crossfire+directx12+ pci v3+ extra power supply?
it turns out that the Reds have vidyuhi for rogue or smart-ass?
what's the point in general?
take a two-headed mother with two vidyuhi and xenons 2690 + radeons 570 + 4 ddr4 channels for a pair of each?
but such a mother from 30000r.? asus.
or juanan ddr3!
I’m just at a loss as to how smart people choose budget vidyuhi but with the latest technologies - just play on tanks 4k + video watch 4k
radeon 570 is it cheap and cheerful, and even for old motherboards?