Is my 2.5 exhaust holding me back?

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I have a basic cammed/stalled/nitrous GTO. On the motor (low 400s) I'm sure the exhaust I have now is more than enough. However on my 150 shot wet kit I'm closer to high 500s low 600s. Could my exhaust be holding me back on spray?

Current exhaust:

Long Tube Headers 1-7/8" primarys, 3" collectors
Catless 3" to 2.5" mids mandrel bent
2.5" mandrel bent catback into straight through mufflers.

Just curious?

I ask the question because I'm shopping for exhaust for my TBSS which has a Maggie on it. Supposedly true dual 2.5" isn't enough for that setup according to those forums, so I'm looking at doing true dual 3" on it to compliment the Kooks I'm about to put on it.

Thanks for any input...