4890 was still on 55nm and early GDDR5 days , a 40nm 800SPs card from 2011 would be A LOT more power efficient, if you look at the 5770 from 2009/2010(850MHz 800SPs 40nm 128bit memory) it was already pretty OK in terms of power draw, although the mobile versions were running lower clocks (700MHz) it was good enough for laptops.
so I think it's more than realistic for a console in 2011, perhaps they could have goeven further, near 1000SPs on 40nm
and it's possible that they would have used VLIW4, but until mid 2012 all APUs were VLIW5... GCN I don't know, the 7970 was available (limited) for purchase in January 2012, probably to soon.
I don't think comparing a PC with "2011" specs would do much good in current games, there is a serious lack of optimization for old Radeons going on (driver support ended officially like 2 days ago, but realistically it's been almost nothing for the past few years with bugs accumulating and not a lot of optimization going on for non-GCN cards) and limited ram capacity, while in a console they would still be heavily optimized for the architecture they were locked to, I think comparing the 6870 with the 7870 with pre-2013 games is a decent way of seeing the difference,
http://anandtech.com/bench/product/780?vs=857
7870 was a 210mm2 GPU, the 6870 a 250mm2 GPU, both with 256bit GDDR5 but higher clocks (and TDP!) for the 7870
or you can compare something closer to the actual PS4 perf (7850) I think and the number of SPs I mentioned earlier, but also less than half the memory bandwidth
http://anandtech.com/bench/product/538?vs=549
looking at the benchmarks, I would think a VLIW5 console with not to far memory bandwidth (and amount of SPs/ROPs/TMUs) could be doing OK with a Witcher 3 or Fallout 4 with some quality reduction but with the same gameplay and mostly visual style, still, some situations could have less than half the performance.
the Wii U is just something else, with rumored 320 or less SPs and 64bit DDR3, from a post earlier, I think even in 2009 or 2010 a PS4 would have easily over 2x the Wii U GPU specs, like the original Wii specs, I don't think it's of any relevance for the other consoles specs.