A few things I would suggest you REALLY Think about here.
E85 compatible cars and built motors have all of the things you listed but there are several more things to take into consideration.
If you look into the platforms that use E85 but are not built to specifically handle E85 you will see they tend to have issues with injector seals after a while due to them drying out. Increased injector failure from what some claim is the higher likely hood for E85 to contain water than standard petrol.
Also blackstome oil reports show 2x as much fuel in the oil over standard cars. In some cases it’s even higher.
You are correct in the fact that the A4 pump is similar and the A4 pump handles more flow but also remember the A4 pump flows more to handle the higher needed percentage of fuel BUT the A4 pump is doing that for a 4 cylinder making about 1/2 the hp with less rpm than something like the RS5 is…
What point am I making. Trying to run straight E85 on non E85 compatible cars in every platform not just Audi has ended up with issues for everyone if run long enough.
Also keep in mind the failure rate of the Audi FSI OEM injectors as it is. The FSI injectors have a pretty high failure replacement rate and it almost looks like the injectors have a life expectancy and should be considered to be replaced after a set amount of miles.
I think if the RS5 was a turbo car or a SC car then sure it makes more sense to run full E85. What I would suggest is running a mixed blend. Its more sustainable and HIGHTLY reduces the negative impact.
Also remember our NA 4.2 motors only need so much octane. While sure my motor is the older gen 4.2 after a while neither our gen or the RS4 gen 4.2 saw any benefit from more octane past a certain point. And that point was about 98 octane… Also the energy release of E85 is reduced per volume over standard petrol. So while your picking up some gain with E85 a lot of it is in its cooling properties after a certain octane point.