Doesn't need full boost to overspeed. EGR will go in at full pedal, just not at very high rpm, so upto 4kish you'll do a lot of damage

I run engine dynos for a living mate - and alter all ECU variables daily, main timing, boost, throttle, MAF (EGR basically) etc

And how MAF/EGR effects the turbo speed (instrumented so you can see the actual speed i,e 240,000rpm ) is very suprising at first