I'd remove the dv as I have never seen one fitted there before in my life, get things back to std, then see what boost does. You may find that dv has a soft spring, in which case it will let boost go early, hence the fact it dies at 4500rpm. If you run boost at anything other than std, dv's often don't reflect that, hence the "dime" trick in the US, where they stiffen the spring by shortening it's length with a dime...
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