Well this is easy to clear up for the OP as I experimented with e85 in all types of mixtures on a completely stock car, with no injector or pump upgrade, no tunes or nothing, simply for the octane and cooling effects.
It makes a HUGE difference and the car is really noticably quicker with 3 gallons of 85 and the rest 91.
The problem however is our injectors and pump simply cannot handle it. Car could not be driven over 7k rpms and would simply sputter like crazy during wot higher than 7k. Or even at 6500 k when going up hill or any additional load on the car.
I tried 2 gallons but essentially did the same only took a bit more load. Higher than that was not even tried.
I was a bit baffled as I know the n54 guys and many cars run it stock without upgrading injectors but I realized the key is that en engine running to 8400 rpm, requires such a mass amount of air and fuel at that rpm that since using e85 requires more fuel to be put out for that air than normal gasoline, it simply could not keep up and sputtered like crazy.
Sad part is the car did feel really damn strong until the engine temp got a bit high and rpms climbed. Took the fun out of the driving for me as I love going to 8400 all day.
Now if you are someone who does not rev the car, you will see a nice pull under 6k rpms. HOwever 1st and 2nd were not usable under WOT. THe load in 1st and 2nd would cause sputering at 4-5k rpms
A high rpm engine in the 8400 range simply has a much more enormous air requirement and such little time for fuel pulses to shoot fuel in, you would need bigger injectors and pump. Which then require a tune etc.
So if you know someone that can tune and someone who can upgrade injectors and pump, i promise you that it makes a huge difference even on a stock car.
I said screw it and now I order 55 gallon drums of 108 unleaded race fuel and mix in 3-4 gallons.
When first doing the e85 and seeing sputtering I went back to normal gas and it went away and then I tried e85 again and same sputer. So it was not a bad batch of e85 or anything.
Essentially our cars cannot run on e20 which is what that mix essentially was. N54 guys are running like 50 percent mixes on stock parts but low revving engines to 6500 really probably requires half as much air and fuel per cycle than does 8400 m3.
So bottom line, can't be done if you want to at all drive the car beyond 3-4k rpm!