Just an update on this I was down to 1/2 a tank of gas of E85, filled up with 91 E10 octane (8 gallons) which puts me at E48. I am able to drive the car up to 16 psi (around 520HP) with no auxiliary fueling, injectors are unplugged. Anything above 16psi and the car doesn't like it. This is with my dual in tank fuel pumps and a boost referenced fuel pressure regulator - I'm at 60psi at idle and around 75-80 psi at WOT in the low pressure side.
Just FYI for MOST guys this is plenty of fuel. I don't know if this upgrade would be enough to run straight E85 on stock turbos BUT the Mazdaspeed guys believe that E48 is the break even point for the benefits of E85. I'm at 23 degrees of timing right now with no knock.
Remember this is transverse motors, the trucks have plenty of low pressure pump AND you can easily swap in a Walbro 420 or 450 pump in the stock location.