In your third video, why does your EWG open at 4500 RPM on stock VF39 turbo? I expect it to open much sooner.
I know you stated you are running the 15.65 psi spring combo, but what is your desired pounds of boost? Your EWG spring combo should be half of desired boost pressure. So with a 15.65 PSI spring combo, I expect you to be looking for 30 PSI?
On my EWG, with Grimmspeed EBCS, I run the 10.5 PSI spring combo running 20 PSI on a VF43. My wastegate cracks at 2800 RPM and is fully open at 3200 RPM. Never had over boosting and have a near straight line that slightly tapers down throughout the RPM range.
My car peaks at 20 PSI.