Ok remembering my GCG Hi-flow was based on an rb25 turbo (bigger turbine housing than rb20).
You will get the turbo spooling around 3000rpm and expect full boost between 4200-4500rpm with a good elc boost controller (full boost being around 15psi), my turbo will hit 20psi at around 4800rpm but has external gate (internal welded up due to an uncommon creep problem) which actually made it slightly laggier for some odd reason!
My turbo made 300rwhp on 20psi, remembering it doesnt need those boost levels on an rb25 to make more power (bastards... lol) but the rb20 needs the higher rpm's and boost levels on the turbo.
With some cam's i believe you can get the boost on quiet abit earlier! And with an rb20 turbine housing that little bit earlier again. Its a great turbo for the street, it does suit an rb25 better but i have no problems with the lag on the old rb20
Now Andrew you better come on the cruise on antilag on friday for tests! We need a driving comparison for the hi-flow performance on an r32 rb20 against an r33 rb25 with more power n more weight!