What all these builds lack compared to new consoles is VRAM size. While PS4 may have GPU processing power of 7850-7870 its equipped with 8GB of shared memory, which is shown by latest console port games reviews, that it is used mainly for graphics.
The card like GTX770 which is much faster than console apu will not be able to deliver the same performance at the same settings only, because it will run out of 2GB of VRAM.
I expect all <3GB cards to age rapidly...
Main memory has been the biggest limitation of the previous generation, so it's understandably that they wanted to avoid it this time around. It's also shared memory, so reaching capacity limits and avoiding resulting conflicts is a big concern.
The biggest reason I suspect that 8 gigs of memory serve is to compensate for the slow hard-drives used. For a while it seemed that DX11 games would stream in data as required, rather than preloading it. But it would appear that most console games didn't want to rely on slow and inconsistent HDD I/O and went the opposite route. This is a fundamental shift of direction away from (texture) streaming, that PCs have yet to match or account for, though most likely having at least 8 gigs of RAM is plenty already. I don't think PC ports will run out VRAM anytime soon. As I understand it: 3, 4 and 6 GB cards serve to occasionally save the GPU some copying to take some strain out of the bandwidth bottleneck, nothing more.
Coincidently the new R9 285 exactly matches the bandwidth of the PS4, though it has a whopping 1.55 times the number of stream processors and just 2 GB of DDR5. AMD appears to have found a way to cut down some of the expensive bandwidth by a significant third, whereas in the past the ratio of memory and processing was almost set in stone.
According to Wikipedia the max. memory bandwidth of the PS3 is 176 GB/s which also puts into into range of the older R7 265 - R9 270x; still above the 153 GB/s of the 7850.