Well, it helped my car because the stageas, and i'm pretty sure all RB25DET's standard run rich, mine is currently at 11:1 A/F. having ethanol increases the amount of oxygen molecules in the fuel, essentially increasing that A/F ratio. i'm not sure if it brings it to the optimal 12:1, but it gets closer.
due to the ethanol having more oxygen, it is therefore more reactive, and it deteriorates the seals and rubber o-rings in the fuel system faster. that's the downer of using ethanol fuel i guess. newer cars don't have the problem, but most skylines being early to mid 90's cars do.
this is pretty much all i know about it, i'm sure other people know more, or know it more correctly than i do.