It's 4% in HWUB's bench, which turns out to be almost as much as the reduction in bandwidth:
To me this indicates that the 4070 is definitely memory bottlenecked in some titles, because if it wasn't you wouldn't have seen a near 1:1 drop-off in performance.
Mind you the performance difference is really besides the point, the fact remains that Nvidia is using cheaper, slower memory while not passing the savings onto the customers or making it clear in the model name.
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The 4070 GDDR6 model consumes 1.52% less power while being 4% slower. It also consumes more power at idle. So overall a small reduction in efficiency.