If 720 gets say GCN2 and PS4 has GCN1? Then 720 needs some API (or lack of API) which exposes what is possible with GCN1 and what is made possible with GCN2. Keep in mind DX11.1 does not even come close to exposing what AMD's GCN GPUs can do. Given a choice between GCN1 GDDR5 and GCN2 with DDR3, the GDDR5 wins every time for me.
Also if one has almost 2x the flops as the other (and has the bandwidth required), then the one with 2x the flops will have a good advantage in pixel quality which translates into either better AA, higher frame-rate, or higher resolution. GPU feature flexibility mostly translates into the capacity for richer content, for instance more objects with different materials. Raw performance is still needed for pixel quality and triangle density per object.
If we go with some wild speculation like GCN2 is a full tiler GPU like PowerVR (taking the EDRAM path to it's logical extreme conclusion), and they have 32MB of on-chip RAM with massive bandwidth (much larger than 256 GB/s), then things like box-filtered MSAA with high resolutions is possible, but triangle density would take a major hit, because you'd need to store all the binned triangles for the scene in that 32MB.