you could always go with a Garret T3/T4 with a S trim wheel....600 cfms@15psi will certainly get you your 300whp mark!
or ..if you don't mind lag...a V trim wheel will certainly put a smile on your face!
since there are many different T3/T4 combos....and I am partial to mitsu turbos,but I have the flow maps to the following Garret turbochargers:
T3 40,45,50,60,super60,61,64,66,68,70,72,76 trims
T04 60 62 trims
To4E 40,46,50,54,57,60 trims
But I'm finding new ones weekly!