my 2 cents ,having driven gcg 450hp hi flow , gt3076 500 hp turbo with a/r .63 internal wastegate and my current set up gt3040 600hp turbo with a/r .82 exhaust housing.
gcg 450p hi flow gave me 230rwkws on 20 psi at 3200rpm. heaps on low end and midrange a great street turbo.
gt3076 500hp turbo gave me 260rwkws on 20 psi at 3500rpm / 3800rpm. three weeks later the engine let go. then i had the engine rebuilt with forged internals and with the addition of tomei poncams step 1s , she pulled 281rwkws on 22psi this was with 8.5 to 1 compression instead of standard 9 to 1. this combination pulled high 12s down the quarter with crap 2.2second 60 footers on street tyres and 112 mph. a great compramise between street and strip!
gt3040 600hp turbo with .82 a/r exhaust housing, tial 38mm external wastegate and highmount manifold plus ported head now gives me 274 rwkws on 15/17 psi and 347 rwkws at 4400rpm fullboost but you feel the kick in the pants from 4000rpm. yet to try this combo out on the dragstrip but i can tell you that from 4400rpm to 4600rpm the power goes from like 168 rwkws to 268 rwks and its breaks traction 1st 2nd 3rd and 4th gear!!! very peaky bitch in deed. luckily though i can turn the boost down from 24psi 347rwkws down to 15psi 274 rwkws and she doesnt come onto boost as hard. hope this help you out, cheers carl.