Well, as far as the stock turbo goes, I think it's an unknown at this point as its an upgrade that is looked at for big turbos. If I had to guess, I'd say you might be able to squeeze 230-240whp out of E85 with a safe tune.
I think it's a fair assessment as the limiting factor in the stock setup is the turbo. Alone it is the primary limiting factor; fueling is secondary.