4GB is what all mid-high end cards last two generations have had minimum of. Its also 25% more ram than 3GB and HBM works much better than GDDR5. You don't see Fury failing @ 4k compared to GDDR5 based cards which tend to lose performance much faster.
I see a Nano 4 FPS slower than a 1070, where is the issue? Or are you trying to compare the $240 reference 480 vs the $300 reference 1060 which have the same FPS?
Yes I turn down settings that make almost no IQ gain but have massive FPS hits. "High" vs "Very High" often look identical when playing and you have to tab back and forth between two still pictures to try to find minute differences.
The difference is, you are paying 30% more, but only getting that 30% difference in some games, in others, it's the same or even slower.
Amazing how that 4GB of VRAM isn't limiting it at 4k Ultra 8x TSSAA. That 3GB 780 Ti though? Not doing so well.