I think 300/300 is very respectable. If perhaps the turbo has more in it, a stiffer wastegate will not only allow you to hold peak boost longer but also possibly make more peak boost pressure and horsepower. In theory people could be running into the is of the wastegate being forced open by the exhaust gases.
Back in the day, turbine housing A/R's were spec'ed per application because internal wastegates were a new technology and added expense. So they would spec a larger A/R exhaust housing when the application needed more power (but lose transient response and spool) and a smaller A/R for when they wanted less power (quicker spool, but higher back pressure which limits peak boost, and peak wheel speed). With the advent of wastegates, it allows you to run a smaller turbine housing to obtain that quick transient response but not overspeed the unit or create too much backpressure and heat. They also serve as a safety device in that it will be forced open if the actuator ever loses vacuum reference or possibly has a leak. In tuning you can try to demand 40psi, but if the wastegate actuator just doesn't have enough spring pressure to keep the wastegate closed under High boost, then it will just automatically start bleeding exhaust gasses which in turn limits peak wheel velocity if the turbine housing can support it.
In testing it showed that on the BorgWarner EFR turbos twin port wastegate flappers, there is so exhaust force exerted onto the wastegate assembly that even if the spring in the actuator can hold it, the bracket supporting the actuator was bending allowing it to open prematurely. Now this was this was an EFR unit that a company was building a kit for and made their own wastegate actuator bracket and not one that came from Borg.