I guess I’m “stupid” then. I still haven’t found another 600+ rwhp NA street driven (easily daily drivable, I just happen to have other cars) LSX. I’m really not sure how my car is not a street car. I drive it to/from the track (some are a full day’s drive away). I take it to work a lot. I drive it for fun up in the hills on the weekend. I’m not sure YOU understand the definition of a street car. I’m pretty sure it’s a car that’s driven on the street, hahaha. I just keep a 91 octane tune handy in case I need it. It’s that simple. Don’t get all hurt just because I’m making more power NA than you are w/ the turbo. 
No, you don’t need E85 or anything to go over 600rwhp on a turbo LSX. At least you shouldn’t. But it’s basically free power so why not? Most turbo guys see around 10% more power on E85, it runs waaaaaaaaaay cooler (which I think would be a big benefit in this car), it basically doesn’t detonate but just stops making power if the tune is off, it keeps the motor cleaner, and it’s cheaper than 87 octane. Why the hell not use it? Like I said, just keep a 91 tune handy and then you’re fine.
-TJ