Not sure about adding E85 to bump 91 or 93, but by adding race gas you'd be gaining thermal stability (always a good thing in a race/stressful enviornment) and that's about it. Now if your car was tuned to take advantage of racegas, that would be a different matter. But it would be kind of silly to spend the money on a racegas tune for a stock car where you can put the money in going stage 2 and have safe, permanent gains.
edit: Errrr, you're already stage 2...soooo I guess upgrade your fuel system and get a proper tune so you can properly take advantage of the E85. Or if you're on the quest for more power put the money towards a new turbo...which will still require a new fuel set-up sooo I dont know what to suggest