Dynojet. "Normally"means normal setup/similar setup to my mods??Which dyno are you going to get your car tuned?
If dynojet, at 1.2bar also normally hits around 260-270whp only, 300whp definitely need 1.5 bar but then the durability of your stock turbo will be affected.
I would say is, just get a bigger turbo
Bigger turbo, would 20g sufficient upgrade? bigger turbo means need to have supporting mod internal parts.?. :hmmmm::hmmmm: