Sard High Pressure Fuel Regulator 200 - 800 kpa

Can this device help me with power gain in my saab b204 engine stage 3 ?

If Yes , what kind of pressure I should set 3.5 or 4 bar or more?

I plan go with Walboro 255 gss 341 or bosch 044 fuel pump + simens dekkas 630, plus holset hx40w

FPR with 200 - 800 kpa range can be helpfull or it will be wasting of money?
( faster engine WOT reaction or only few HP more )

Regards
danny