First off, I'm running both of them.
Unless you play that 50% higher title, it's misleading, that titles probably been added to make it look a higher performance delta.
If the 70 is maxing@60 fps and the 80 maxing@72 fps, yes thats 20% higher fps on same settings.
As stated above, add 2 higher in game settings(it could be 3 settings, but it could also only be 1 setting)-they both hit 60 fps-it isn't a huge difference imo.
Anyone buying either 70/80 should be aware if Nv's Ada baseline vram amount is increased to 12Gb, both the 70/80 are toast going forwards imo, they will still run everything but on lower settings.