As long as you have good enough wiring the Walbro 450 would be fine.....in E85 i don't think there are many other options from walbro......and i wouldn't trust anything else as an in-tank main pump, it does sound like you have a lazy pump....
China
FPR's...
Nick73, 350Kpa is 50 psi, about right(higher than stock 300Kpa) for a base pressure for 1000cc injectors to aid atomisation.
You could bench test your fuel system somewhat, use an airline on the
FPR and pump 2 bar into it with a base pressure of 350 Kpa... see if it gets to 550Kpa, then if you want to simulate injectors working in the mix add a 1mm hole bleed into a container and do same test, you can then play around and test pump current and voltage etc.(current would tell a lot...pump should go rated max current, under or over by too much and its no good)