Stock 8mm fuel line will do/has done well over 600whp, i think even 700whp(thats well over 850fwhp) on e85 might happen.....just need a pump that can keep up.
What
FPR ?
If your pump and reg work right there should be no pressure drop ... fp should be solid base setting plus map until you let go of throttle.
Put a walbro e85 pump in it ! ...does sound like pump is lazy.