You are just mentioning what is necessary.
And is true only in many games so long as they don't benefit from rebar/sam or you are framerate limited:
AMD Smart Access Memory Tested, Benchmarked | TechSpot Sam and rebar should both also work on PCIe3, but they don't and won't just like whatever new thing won't work on gen4.
But even 2-5% will be larger than the benefit of a faster, yet still 100% GPU bound CPU.
You know they have to compare these things on 1080p low, 720p to see which is faster they are so GPU bound.
PCIe4 has been made a selling point. I'm just saying PCIe5 will as well. Or else why would anybody buy a Zen4 that isn't a Threadripper or Epyc?