Which oil pump to buy?

Ok guys engine time and need to decide what oil pump to run . Looking at 400bhp territory so decided to stick a better pump in. Now anyone got experience they can share as theres a few choices
Rcm modified pump ( would it be enough)
Rcm uprated hi flow pump
Cosworth pump
Stardard modded pump with new valve ?

Then there 11mm 12mm ect lol
Bit of a mine field this impreza rebuild like haha. Nice learning curve none the less

Cheers